Autossh

2010-07-25T14:11:37Z

Jcllings:

So maybe your having trouble keeping an ssh tunnel open for a program you want to secure. Lets say it's synergy, which uses port 24800. I recommend using autossh for this:

autossh -f -v -M 24800 -N -R 24800:localhost:22 remotehostname

Reason being that autossh will automatically restart the tunnel if something pesky wacks it.

Jcllings: /* Technologies */

= Introduction =
If you type in a rather long and complex [[command]] at the [[command line]], you might want to save that command in a [http://en.wikipedia.org/wiki/Text_file text file], so you can execute it later without having to type the whole long thing in again. If you add a line to the beginning of that file, like "<tt>#!/bin/bash</tt>" (a so-called "[[shebang]]" line), and then make the file executable with the <tt>[[chmod]]</tt> command, you've just created a shell script.

Here's an example shell script:
#!/bin/bash
# Any line that starts with a hash, besides the shebang line, is a comment.
echo "Hello world!"

You run the [[shell script]] just like any other [[executable]]. Some folks create a <tt>bin</tt> directory in their home directory within which to place their scripts. Others drop them in <tt>/usr/local/bin</tt>.

Some key points to keep in mind about shell scripts:
* They execute their commands, line by line, just as if you'd typed them in yourself at the command line.
* The commands in the script run in a subshell of the shell from which you executed the script.
* If you want the script to affect your [[pwd|present working directory]] or [[environment variables]], source it with <tt>. scriptname</tt>.
* Don't put spaces around equal signs.

You can check out the [[bash]] page and you'll also find lots of info in the [http://www.tldp.org/LDP/abs/html Advanced Bash-Scripting Guide].

= Technologies =

== Handy Things To Know ==

Using '''set -e''' in your script will cause it to drop dead on the first error. This is a good thing when manipulating an operating system, file system or if the script otherwise runs very long. Basically, when ever a return value that isn't 0 comes back from a command, it stops the script. Be careful though, this is not necessarily an error condition. The '''grep''' command, for example, returns 1 when it doesn't find anything... but then maybe that is what you are counting on! The consequence will be that you script will stop and you may not immediately understand why.

==Color Prompts==
Tip: '''dircolors''' is a bash command of interest for folks who want to colorize the output of the '''ls''' command.
For more on color prompts, check out [http://wiki.archlinux.org/index.php/Color_Bash_Prompt Color Bash Prompt at ArchWiki].

== Using quotes ==
Quotation marks, either double quotes (") or single quotes ('), are often needed in shell scripts to pass arguments that have spaces or other special characters. The two quotes have slightly different meanings. Single quotes protect the exact text they enclose.

Inside double quotes, the dollar sign ($) is still special, so shell variables and other $ expressions are interpreted, as is the backquote (`) used for command substitution. Lastly, the backslash (\) is special in double quotes, so be cautious. Some examples and the shell output of each:

$ echo 'The location of the shell is stored in $BASH'
The location of the shell is stored in $BASH
$ echo "The location of the shell is $BASH"
The location of the shell is /bin/bash
$ echo '\\'
\\
$ echo "\\"
\

== Return values ==
The return value, also known as error code, delivers the exiting state of the most recently executed program. It is defined to be 0 in case no error happened. It is stored in the variable $?:
scorpio:~ # echo "hello world"
hello world
scorpio:~ # echo $?
0
scorpio:~ # ls /doesNotExist
/bin/ls: /doesNotExist: No such file or directory
scorpio:~ # echo $?
2

The [ ] operators deliver 0 if they contain a true expression, 1 if they contain a false expression:
scorpio:~ # [ 5 = 5 ]
scorpio:~ # echo $?
0
scorpio:~ # [ 5 = 6 ]
scorpio:~ # echo $?
1
scorpio:~ #
Here, [ is a [[command]]. A command requires a blank behind it - thus the following error is very common:
scorpio:~ # [5 = 6]
bash: [5: command not found
Also the ] requires a blank in front of it:
scorpio:~ # [ 5 = 6]
bash: [: missing `]'
The "=" sign requires a blank in front of it and after it. Otherwise, the bash only sees "something" within the brackets, and that is true (0), while "nothing" is false (1):
scorpio:~ # [ aoei ]
scorpio:~ # echo $?
0
scorpio:~ # [ 5=5 ]
scorpio:~ # echo $?
0
scorpio:~ # [ ]
scorpio:~ # echo $?
1
scorpio:~ # true
scorpio:~ # echo $?
0
scorpio:~ # false
scorpio:~ # echo $?
1
You can hand over your own error codes with the command exit. This command will exit from the current process. As the ( ) signs spawn out an own process, you can do the following:
scorpio:~ # (exit 5); echo $?
5

== Conditions ==
Conditions are handled with the [[if]] command, using the form
if <expression>
then command1
else command2
fi
"fi" as the reverse of "if", closes the loop.
bash allows you to substitute newlines with ";", so the following form is also legal:
if <expression>; then command1; else command2; fi
Example:
scorpio:~ # if true; then echo "yes"; else echo "no"; fi
yes
scorpio:~ # if false; then echo "yes"; else echo "no"; fi
no
You can omit the else-branch:
scorpio:~ # if [ 5 = 5 ]; then echo "five is five"; fi
five is five
scorpio:~ # export name=Thorsten
scorpio:~ # if [ $name = Thorsten ]; then echo "it's you"; fi
it's you
In this case, bash replaces $name with its content. That means, we get an error if $name is empty:
scorpio:~ # export name=
scorpio:~ # if [ $name = Thorsten ]; then echo "it's you"; fi
bash: [: =: unary operator expected
scorpio:~ # if [ = Thorsten ]; then echo "it's you"; fi
bash: [: =: unary operator expected
To overcome this problem, one can add an "x" to the left and to the right:
scorpio:~ # export name=Thorsten
scorpio:~ # if [ x$name = xThorsten ]; then echo "it's you"; fi
it's you
scorpio:~ # export name=
scorpio:~ # if [ x$name = xThorsten ]; then echo "it's you"; fi
scorpio:~ #

== Negations ==
You can invert true/false values with the ! operator:
$ ! true
$ echo $?
1
That helps you if you want to do "not"-statements:
if ! [[grep]] "network error" /var/log/messages
then [[echo]] "There is no network error mentioned in the syslog"
fi
The ! is just like a [[command]] with arguments, that's why it is important to have a space behind it:
$ !true
bash: !true: event not found

== Loops ==
You can [[loop]] on a condition:
while [ 5 = 5 ]; do echo "This never stops"; done

until [ 5 = 6 ]; do echo "This never stops"; done

== $-variables ==
:$! : PID of last [[process]] that has been started in the [[background]] (e.g. firefox &)
:$? : return value of last [[command]]

== Counting ==
x=0; ((x++))
x=0; x=$((x+1))
x=0; let x=$x+1
for (( x=0; x<10; x++ )) ; do echo $x ; done

for x in $(seq 0 9); do echo $x; done
x=0; x=$(expr $x + 1)
x=0; x=$(echo $x + 1|bc)
x=4; x=$(echo scale=5\; $x / 3.14|bc)

The first four demonstrate Bash' internal counting mechanisms, these will not use external programs and are thus safe (and fast).
The last four use external programs. [[bc]], as used in the last two examples, is the only one that supports numbers with decimals. For adding, subtracting and multiplying, you don't have to do anything special, but for division you need to specify the number of digits to keep (default is none) using the 'scale=n' line.

== Combining multiple conditions of if statements ==
AND:
if((a==1 && b==2))
OR:
if(( a!=1 || b>10 ))

== Conditional execution ==
As stated above, you can do something like
scorpio:~ # if (( 5 == 5 && 6 == 6 )); then echo "five is five and six is six"; fi
five is five and six is six
We call 5 == 5 the left term and 6 == 6 the right term. [[Bash]] first evaluates the left term and if it is true, it evaluates the right term. If both are true, the result is true, otherwise, the result is false (boolean logic). It is an interesting effect that, if the left term is false, the right term is not even evaluated - the result will be false in any case. That means, if we replace the terms by commands, the right command will only be executed if the left command succeeded. One can use this effect:
scorpio:~ # ls > /tmp/dir && echo "the command succeeded"
the command succeeded
scorpio:~ # ls > /proc/cmdline && echo "the command succeeded"
/bin/ls: write error: Input/output error
scorpio:~ #
In the above example, bash tells you if the command succeded. The right command is conditionally executed.
Considering a famous saying, you can even program a bird using this technology:
eat || die
This line says "eat or die" which is very useful if you want a program to exit in case it cannot perform a certain operation:
touch /root/test || exit

== Functions ==
You can define functions for [[structured]] [[programming]]. It is also possible to hand over parameters to a function.
Example:
#!/bin/bash
# This program calculates the square of a given number

function square \
{
echo "The square of your number is "
echo $((a*a))
}

echo "Input a number"
read a
square $a

= UseCases =

== Renaming a set of files ==
The following example will rename all files ending in .jpeg to end in .jpg
$ for file in *.jpeg; do mv $file ${file%.jpeg}.jpg; done

[[mmv]] is a really nifty tool for doing this sort of thing more flexibly too. The [[rename]] command also provides similar functionality, depending on your linux [[distribution]].

If you have a load of files in all capital letters (common if you unzip old [[DOS]] programs for instance), you can use
$ for file in *; do mv $file $(echo $file | tr upper: lower:); done
to make all the files in the current directory lowercase.

== Get your IP address ==
A [[bash]] example to get your IP address using http://www.whatismyip.com: 
lynx -dump http://www.whatismyip.com | grep -i "Your IP is" | awk '{ print $4; }'

Or use this:
$ ifconfig ppp0 | awk '/inet addr/{print $2}' | cut -d: -f2

Or this:
$ ifconfig ppp0 | sed -rn 's/^.*inet addr:([^ ]+).*$/\1/p'
Note that ppp0 stands for the first point-to-point-protocol device which is usually a modem. If you are using an ethernet adapter instead, replace ppp0 with eth0. You can also leave it out all together to list all the addresses associated with your computer.

== Converting several wav files to mp3 ==
This statement will convert all .wav files in a directory to mp3 (assuming you already have the [http://lame.sourceforge.net/ lame] mp3 encoding [[package]] [[install]]ed):
for i in *.wav; do lame -h $i [[&&]] rm $i; done
The double ampersand prevents rm from deleting files that weren't successfully converted.

== Full file name ==
Prints the full filename removing ./ and ../ and adding `pwd` if necessary.

'''fqn.sh'''
<pre>
#!/bin/sh

# return the full filename, removing ./ ../ adding `pwd` if necessary

FILE="$1"

# file dot relative
# ./file dot relative
# ../file parent relative
# /file absolute
while true; do
case "$FILE" in
( /* )
# Remove /./ inside filename:
while echo "$FILE" |fgrep "/./" >/dev/null 2>&1; do
FILE=`echo "$FILE" | sed "s/\\/\\.\\//\\//"`
done
# Remove /../ inside filename:
while echo "$FILE" |grep "/[^/][^/]*/\\.\\./" >/dev/null 2>&1; do
FILE=`echo "$FILE" | sed "s/\\/[^/][^/]*\\/\\.\\.\\//\\//"`
done
echo "$FILE"
exit 0
;;

(*)
FILE=`pwd`/"$FILE"
;;
esac

done
</pre>

== Resolving a link ==
This little script follows symbolic links wherever they may lead and prints the ultimate filename (if it exists!) (note - it uses the previous script <tt>fqn.sh</tt>)

<pre>
#!/bin/sh

# prints the real file pointed to by a link
# usage: $0 link

ORIG_LINK="$1"
LINK=`fqn "$1"`
while [ -h "$LINK" ]; do
DIR=`dirname "$LINK"`

# next link is everything from "-> "
LINK=`ls -l "$LINK" |sed "s/^.*-> //"`

LINK=`cd "$DIR"; fqn "$LINK"`
if [ ! -e "$LINK" ]; then
echo "\"$ORIG_LINK\" is a broken link: \"$LINK\" does not exist" >&2
exit 1
fi
done
echo "$LINK"
exit 0
</pre>
This is a lot simpler, and just as useful (but doesn't do dead link checking)
<pre>
#!/bin/bash
ORIG_LINK="$1"
TMP="$(readlink "$ORIG_LINK")"
while test -n "$TMP"; do
ORIG_LINK="$TMP"
TMP="$(readlink "$ORIG_LINK")"
done
echo "$ORIG_LINK"
</pre>

== Viewing a file according to its type ==
I save this as a script called <tt>v</tt> and it is my universal viewing script - it can be extended to any kind of file and to use your favourite tools for each type of file. It uses the <tt>file</tt> utility to determine what sort of file it is and then invokes the correct tool. It automatically adapts to being used on the system console or under X.

(note - this uses a prior script <tt>fqn.sh</tt>)
<pre>
#! /bin/sh
# View files based on the type of the first one:
# Relies partly on 'less' to invoke an appropriate viewer.
# Make sure than you have this set:
# LESSOPEN="|lesspipe.sh %s"

FIRST="$1"
FULL=`fqn $FIRST`

# if we are being piped to, just run less
[ -z "$FIRST" -o ! -r "$FIRST" ] && exec less "$@"

# some file types beyond what /usr/bin/lesspipe.sh handles:
case "$FIRST" in
*.cpio.bz2) bunzip2 -c $1 | cpio -ctv 2>/dev/null |less; exit ;;
*.cpio) cpio -ctv $1 2>/dev/null |less; exit;;
esac

TYPE=`file -L -i "$FIRST" 2>/dev/null | \
awk '{len=length("'"$FIRST"'")+ 2; $0=substr($0, len); print $1;}'`
echo "Type=\"$TYPE\""
case "$TYPE" in
image/jpeg | image/tiff | image/gif | image/x-xpm | image/*)
xzgv "$@" ;;
application/pdf)
XPDFGEOM=`xdpyinfo |awk '/dimensions/ {print $2}'| \
awk -Fx '{printf("%dx%d+0+0", 0.60*$1, $2-35)}'`
xpdf -geometry $XPDFGEOM -z width "$@"
;;
application/postscript)
gv "$@" ;;
application/msword)
if [ -z "$DISPLAY" ] ; then antiword "$@" | \
less; else soffice "$@" & fi ;;
text/html)
if [ -z "$DISPLAY" ] ; then lynx "$@"; else dillo "$FULL" & fi ;;
audio/mpeg)
mpg123 "$FIRST" ;;
*)
less "$@" ;;
esac
</pre>

== Finding the 50 largest directories ==
du -S / | sort -nr | head -n50

== Auto-generating a shebang line ==
(echo -n '#!'; which perl; tail -n+2 foo) > bar
This will print "#!" and the path to <tt>perl</tt>, then everything except the first line (the original shebang) of the file <tt>foo</tt>; and redirect all that to go into a file <tt>bar</tt>.

This is really meant for use in install scripts; obviously you know where perl is on your system, but not necessarily on anybody else's system (though <tt>/usr/bin/perl</tt> is a safe guess). But you know bash is always at <tt>/bin/bash</tt>. So, instead of just saying in the documentation "change the first line .....", you can write a little shell script that puts the correct shebang line in the file and copies it to <tt>/usr/local/bin</tt>. Then, put this script in a .tar.gz file with your perl script and any documentation.

== Creating an audio CD from .mp3 files ==
This little script requires the mpg123 and [http://cdrdao.sourceforge.net/ cdrdao] packages. It uses mpg123 to create a .wav file from each mp3 in the current directory, and builds up a "TOC" file (Table Of Contents) as it goes along, using the && notation to be sure only to include successfully-converted files. Finally, it starts writing the CD.

The TOC file is given a name based on the PID, and is placed in the current directory. Neither it nor the .wav files will be deleted at the end of the script, so you can always burn another copy of the CD if you want.

<pre>
#!/bin/sh
tocfile="cd_$$.toc"
echo "CD_DA" > $tocfile
for i in *mp3
do wav="`basename $i .mp3`.wav"
mpg123 -w$wav $i\
&& echo -en >>$tocfile "TRACK AUDIO\nFILE \"$wav\" 0\n"
done
echo -e "TOC file still available at $tocfile"
cdrdao write $tocfile
</pre>

Note: in the <tt>for</tt> statement, you might think at first sight that
it should be <tt>for i in *.mp3</tt>; but Linux doesn't care about
filename extensions at all. * will match a . character; therefore, *mp3
will match everything ending in mp3 or .mp3. Those characters are unlikely
to be found on the end of anything but an mp3 file.

== Portable Indirection ==
Sometimes you need to use the value of a variable whose name is held in another variable. This is indirection. For example:
for V in PATH LD_LIBRARY_PATH; do echo ${!V}; done
but that isn't portable to older shells, eg. the old Bourne shell. A portable way is to use the following instead of <tt>${!V}</tt>:
`eval echo \\$"$V"`
It's not pretty but at least it works on nearly all Unixes.

[ someone said - "It does require that the variable be exported." Actually no. It works without exporting V on bash and on Solaris sh ]

== Matching Curly Brackets ==

If you indent your C, Perl or PHP code in what is commonly called "K&R style", which is to say something like this
<pre>
# nested loop example
for ($i = 0; $i <= 6; ++$i) {
for ($j = 0; $j <= $i; ++$j) {
print "$i : $j ";
};
print "\n";
};
</pre>
i.e. where the opening curly bracket appears on the same line as the flow-control keyword (if, while &c.) and everything up to, but not including, the closing curly bracket is indented, then you may find this useful. I came up with it out of necessity, and thought it was just too important not to share. All it does is display the lines with a { but no following } (in Perl, these denote associative array indexes) or a } with no preceding {. In other words, just the opening and closing lines of loops, not the content. This can help you to spot those annoying missing-bracket errors.

[[awk]] '/({[^}]*$)|(^[^{]*})/{print}' ''foo''

Replace ''foo'' with the filename to be examined. Or, of course, you can omit the filename and use the command in a [[pipe]]line.

The above example would appear as
<pre>
for ($i = 0; $i <= 6; ++$i) {
for ($j = 0; $j <= $i; ++$j) {
};
};
</pre>

== rpminfo ==
This is a small script that prints useful info about an [[rpm]] package. It was inspired by the ability of [[less]] to give almost useful info about an rpm file through <tt>lesspipe.sh</tt>.

#!/bin/sh
echo INFORMATION: ; rpm -qi $* ; echo
echo REQUIRES: ; rpm -qR $* ; echo
echo PROVIDES: ; rpm -q --provides $* ; echo
echo FILELIST: ; rpm -qlv $*

Save it to a file called <tt>rpminfo</tt> in your [[path]] and [[chmod]] it so it's executable. It is often useful to [[pipe]] the output to [[less]], as in the examples below.

To get info on an installed package, you can just give the package name like:
rpminfo XFree86 |less
For a package file that you have just downloaded, give the <tt>-p</tt> [[command options|command option]], just like <tt>rpm</tt>:
rpminfo -p XFree86-4.1.0-25.i386.rpm |[[less]]

== Finding All Files That Start With a '.' (period) ==
To list all the [[file]]s in your current [[directory]] whose file names start with a '.')
[[ls]] -A | [[grep]] -E "^\.\.*"

The following command will copy, overwriting existing files, the hidden contents of the present directory (files and directories that start with a period) into the folder, '/tmp/testing' (assuming that you've already made the target directory):

(Useful for backing up hidden files and directories in your home folder; be sure to change the target directory to something more sensible, though.)

[[cp]] -vfr `ls -A | grep -E "^\.\.*"` -t /tmp/testing/

== Connecting to a wireless access point through Bash (no encryption key)==
To connect to a [[wireless]] access point through the shell, first determine the designation of your wireless adapter:

[[cat]] /proc/net/wireless

This should give you a similar output:

Inter-| sta-| Quality | Discarded packets | Missed | WE
face | tus | link level noise | nwid crypt frag retry misc | beacon | 22
wlan0: 0000 57. -53. -87. 0 0 0 0 0 0

In this case the designation of the wireless adapter is '''wlan0'''. Now you can proceed to the next step, scanning the available wireless points:

[[sudo]] iwlist wlan0 scan

An example of the output you should get:

wlan0 Scan completed :
Cell 01 - Address: 00:1D:8B:52:2C:9C
Channel:6
Frequency:2.437 GHz (Channel 6)
Quality=57/70 Signal level=-53 dBm
Encryption key:on
ESSID:"costa reina"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=000000208e5ce217
Extra: Last beacon: 110ms ago
IE: Unknown: 000B636F737461207265696E61
IE: Unknown: 010882848B960C121824
IE: Unknown: 030106
IE: Unknown: 2A0104
IE: Unknown: 32043048606C
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
IE: Unknown: 0706495420010E10
Cell 02 - Address: 00:1C:A2:B0:DC:54
Channel:1
Frequency:2.412 GHz (Channel 1)
Quality=36/70 Signal level=-74 dBm
Encryption key:on
ESSID:"FASTWEB-1-001CA2B0DC54"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=00000000ddf7c3e4
Extra: Last beacon: 3240ms ago
IE: Unknown: 0016464153545745422D312D303031434132423044433534
IE: Unknown: 010882848B960C121824
IE: Unknown: 030101
IE: Unknown: 2A0104
IE: Unknown: 32043048606C
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
IE: Unknown: 0706495420010E10
Cell 03 - Address: 00:1C:A2:C3:DF:CC
Channel:6
Frequency:2.437 GHz (Channel 6)
Quality=32/70 Signal level=-78 dBm
Encryption key:on
ESSID:"FASTWEB-1-001CA2C3DFCC"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=00000000087f0232
Extra: Last beacon: 2850ms ago
IE: Unknown: 0016464153545745422D312D303031434132433344464343
IE: Unknown: 010882848B960C121824
IE: Unknown: 030106
IE: Unknown: 2A0104
IE: Unknown: 32043048606C
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
IE: Unknown: 0706495420010E10

The important bits of information are: '''ESSID''', '''Channel''', '''Encryption key''', and '''Mode'''. ESSID is the name given to the wireless point. Now you select which one you want to connect to. Let's say you want to connect to an access point that has the following information:

Cell 03 - Address: 00:1C:A2:C3:DF:CC
Channel:6
Frequency:2.437 GHz (Channel 6)
Quality=32/70 Signal level=-78 dBm
Encryption key:off
ESSID:"connect here"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Mode:Master
Extra:tsf=00000000087f0232
Extra: Last beacon: 2850ms ago

The command to connect would be:

[[sudo]] iwconfig wlan0 essid "connect here" mode managed channel 6 key off

Followed by:

[[sudo]] dhclient

*Please note that if there is an encryption key encrypted with WPA, things become slightly more complicated. You can refer to a [http://ubuntuforums.org/showthread.php?t=1342833 script] I wrote for WPA encrypted connections.

= See also =
* [[ShellScripts]]

User:Jcllings

2010-05-24T03:58:31Z

Jcllings: Created page with 'This is my BASH scriptorium and the place where I keep notes on writing them. BASH, is the Borne Again SHell. BASH is a programming language that one writes to execute commands o…'

This is my BASH scriptorium and the place where I keep notes on writing them. BASH, is the Borne Again SHell. BASH is a programming language that one writes to execute commands on a Linux or Unix system. The official BASH website is [http://www.gnu.org/software/bash here]. BASH is an interpreted language which means it runs on a virtual machine like Java does. Unfortunately, BASH isn't all that cross-platform. For the most part, it is for Unix only. Mac's do come with it, by the way. One can run BASH on Windows but you need [http://www.cygwin.com/ Cygwin] for that particular trick. Cygwin can be a little tricky to install, for Windows software but if you're careful to follow the instructions, it shouldn't be a problem. Documentation is fair for Cygwin.

While BASH is the grand Unix standard, it isn't the best language to be writing scripts in these days. It is important for any Unix person to be able to read and trace through BASH, however, because you may need these skills if something goes wrong on your machine. To my knowledge, Ruby is the scripting language currently in favor amongst my peers. I should probably learn it someday.

[[User:Jcllings|Jcllings]] 06:47, January 24, 2010 (UTC)
==Trashy Scripting==

Moved to: [http://wiki.linuxquestions.org/wiki/Scripts LinuxQuestions Wiki - Scripts]

==Scripting Tips==
Using '''set -e''' in your script will cause it to drop dead on the first error. This is a good thing when manipulating an operating system, file system or if the script otherwise runs very long.

[[User:Jcllings|Jcllings]] 06:47, January 24, 2010 (UTC)

==Color Prompts==
See the links section below for a marvellous article on colourized BASH prompts.

Tip: '''dircolors''' is a bash command of interest for folks who want to colourize the output of the '''ls''' command.

[[User:Jcllings|Jcllings]] 06:46, January 24, 2010 (UTC)

==Links==
*[http://wiki.archlinux.org/index.php/Color_Bash_Prompt Color Bash Prompt - ArchWiki]

[[User:Jcllings|Jcllings]] 06:46, January 24, 2010 (UTC)