Shell functions are declared using this syntax: [ function ] name () compound-command [ redirectio... Example: function ll { ls -alF $* } Example 2: ll() { ls -alF $* } Shell functions can be exported to subshells with the -f switch: $ export -f ll However , I had problems logging in Ubuntu 11.10 after I added this to .profile : export -f ll

This is the command to print all regular files in the src folder but excluding all files within the .svn folders: $ find src -name .svn -prune -o -type f -print where -o is the or operator. Define a shortcut: ff () { find $1 -name .svn -prune -o -...

The MIPS CPU is able to run both big-endian and little-endian. So a system built on MIPS can be either big-endian (mips) or little-endian (mipsel). The file command shows the architecture: $ file ls ls: ELF 32-bit LSB executable, MIPS, ... but readelf will tell the endianness: $ readelf -h ls ELF Header: Magic: 7f 45...

To check a command exists on PATH: Use the return code of which : which some_command &>/dev/null [ $? -eq 0 ] || ... For bash, use type -P : type -P some_command &>/dev/null && echo "ome_comm... or check_path() { if ! type -P $1 &> /dev/...

String comparison operators: Operator Meaning -n str the length of str is nonzero. -z str the length of str is zero (0). str1 = str2 str1 and str2 are the same (note one equal sign, not two!). str1 != str2 str1 and str2 are not the same. str str is not a null string Examples: # empty string is not null if [ '' ]; then ... Numerical comparisons ( integer expressions only! ): Operator Meaning int1 -eq int2 int1 and int2 are numerically equal int1 -ne int2 int1 and int2 are numerically NOT equal int1 -gt int2 int1 is greater than int2 int1 -ge int2 int1 is greater than or equal to int2 int1 -lt int2 int1 is less than int2 int1 -le...

Got "base64: invalid input" error: $ base64 -d base64_encoded.txt >original.bin ba... which can be easily dismissed as "input is invalid base64 encoded" or "partial input". But I know it's valid base64 encoded input! The problem was, the input was base64 encoded on Windows! The error goes away after converting to Unix format with dos2unix . dos2unix < base64_encoded.txt | base64 -d >origina... Version of base64 used: $ base64 --version base64 (GNU coreutils) 8.5 ...

grep is a versatile command with many variations (grep, egrep, fgrep, then various implementations). It uses a regula expression (regex) pattern to filter input. But then there are basic and extended flavors of regex - leading to even more confusion. And, beware that there are lots of bad examples of regex in the wild... There are two critical questions to ask when you use grep: which grep implementation are you using? what is the flavor of the regex? Here are some examples for gnu grep v2.7: # Find all numbers (no decimal point), basic regex... Use the -o flag to show only the matching part instead of the whole matching line: grep -o -E '\b[0-9]{2}\b' The good thing about the gnu grep is that it...

The Unix shell passes these parameters to the shell script: Variable Meaning $* A single string representing all command line arguments separated by $IFS (internal field separator, usually a space) $@ A sequence of strings representing the command line arguments. $1,$2...$n $1 is the first argument, $2 is the second argument, and so on... $0 The name of the script itself. $# The number of arguments. Example shell script ( sharg.sh ): #!/bin/sh echo $# arguments passed to $0: $@ ... Output for ./sharg.sh "a b c d" : 1 arguments passed to ./sharg.sh: a b c d here ... Output for ./sharg.sh a "b c" d : 3 arguments passed to ./sharg.sh: a b c d here ...

This is the crontab to run a cron job every 15 minutes: */15 * * * * /path/to/executable >/redirect/output... or, 0,15,30,45 * * * * /path/to/executable >/redirect/... In general, the format is: minute hour day_of_month month day_of_week command Valid values are: Field Value minute 0-59 hour 0-23 day of month 1-31 month 1-12 day of week 0-6 (Sunday = 0) Reference: crontab(5) - Linux man page

Compile mod_proxy_html from source code. Prerequisite: Apache httpd installed on system with header files. Command: # /usr/local/apache2/bin/apxs -i -c -I/usr/local/i... Output: /usr/local/apache2/build/libtool --silent --mode=c...