Tag Archives: Bash Script

Get captured groups from a regex match against a string a='I am a simple string with digits 1234' pat='(.*) ([0-9]+)' [[ "$a" =~ $pat ]] echo "${BASH_REMATCH[0]}" echo "${BASH_REMATCH[1]}" echo …

Checking the syntax of a script with “-n” The -n flag enables you to check the syntax of a script without having to execute it: ~> $ bash -n testscript.sh …

Modifying filename extension $ mv filename.{jar,zip} This expands into mv filename.jar filename.zip . Create directories to group files by month and year $ mkdir 20{09..11}-{01..12} Entering the ls command will …

Colorize and customize terminal prompt This is how the author sets their personal PS1 variable: gitPS1(){ gitps1=$(git branch 2>/dev/null | grep '*') gitps1="${gitps1:+ (${gitps1/#\* /})}" echo "$gitps1" } #Please use …

Simple completion using function _mycompletion() { local command_name="$1" # not used in this example local current_word="$2" local previous_word="$3" # not used in this example # COMPREPLY is an array which …

Compare two files from the web The following compares two files with diff using process substitution instead of creating temporary files. diff <(curl http://www.example.com/page1) <(curl http://www.example.com/page2) Feed a while loop …

Dynamic scoping in action Dynamic scoping means that variable lookups occur in the scope where a function is called, not where it is defined. $ x=3 $ func1 () { …

Parameter DetailsEXPRESSION Expression to evaluate Simple arithmetic with (( )) #!/bin/bash echo $(( 1 + 2 )) Output: 3 # Using variables #!/bin/bash var1=4 var2=5 ((output=$var1 * $var2)) printf "%d\n" …

Math using dc dc is one of the oldest programs on Unix. It uses reverse polish notation, which means that you first stack numbers, then operations. For example 1+1 iswritten …

Quick Reference Interaction with the history # List all previous commands history # Clear the history, useful if you entered a password by accident history -c Event designators # Expands …