Bash shell scripting

Links

• Bash Guide for Beginners
• Colors for echo

Parameters

   $$ PID of the process
   $? exit status
   $0 call of the current script
   $1 1st parameter
   $2 2nd parameter
   $n etc...
   $* all parameters
   $# parameter count

|| and && - status based commands

Syntax:

 normal-command && if-succeeded || if-error

Example:

 rm /bla  && echo ok || echo not ok;echo Done

Will normally output:

 rm: cannot remove `/bla': No such file or directory
 not ok
 Done

Attention:

 rm /bla && echo ok ; echo really ok || echo not ok ; echo shit

Will output

 rm: cannot remove `/bla': No such file or directory
 really ok
 shit

So || and && will only work for the last command and will only work for the next command.

While on console

while true; do echo -n `date`;ls -l <file>; sleep 1; done;

parameter check

if [ "$1" = "--help" ] || [ $# -ne 1 ]; then
    echo my script v 0.1, it's me !
    echo This script will do some cool stuff but I won't tell you what.
    echo Syntax: $0 \<file\> \<whatever\>
    exit 1
fi

do something depending on output/no output of a command

#!/bin/bash
for file in ~/work/Sx*
    do
        cd $file
        out=$(cvsupdate)
        if [ "$out" != "" ]; then
            pwd
            echo "$out"
        fi
done    

Use the double quote for the echo or you will lose all line breaks.

get the absolute directory of the executing script

#!/bin/bash
DIR=$(cd `dirname $0` && pwd)
echo $DIR

Remove the first/last character

First character:

echo super | sed 's/^.//'

Last character:

echo super | sed 's/.$//'