Linux

The -e conditional operator tests whether a file exists (including all file types: directories, etc.). if [[ -e $filename ]]; then echo "$filename exists" fi There are tests for specific …

Double quotes for variable and command substitution Variable substitutions should only be used inside double quotes. calculation='2 * 3' echo "$calculation" # prints 2 * 3 echo $calculation # prints …

Execute command with here document ssh -p 21 example@example.com <<EOF echo 'printing pwd' echo "\$(pwd)" ls -a find '*.txt' EOF $ is escaped because we do not want it to …

Sourcing a file Sourcing a file is different from execution, in that all commands are evaluated within the context of the currentbash session – this means that any variables, function, …

OptionMeaning-uMake each lines of output unique Sort command output sort command is used to sort a list of lines. Input from a file sort file.txt Input from a command You …

OptionDescription-a,-archiveCombines the d, p and r options-b, -backupBefore removal, makes a backup-d, –no-deferencePreserves links-f, –forceRemove existing destinations without prompting user-i, –interactiveShow prompt before overwriting-l, –linkInstead of copying, link files instead-p, …

The $ character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to …

Functions with arguments In helloJohn.sh: #!/bin/bash greet() { local name="$1" echo "Hello, $name" } greet "John Doe" # running above script $ bash helloJohn. Hello, John Doe If you don’t …

Examining assoc arrays All needed usage shown with this snippet: #!/usr/bin/env bash declare -A assoc_array=([key_string]=value \ [one]="something" \ [two]="another thing" \ [ three ]='mind the blanks!' \ [ " four" …

Array Assignments List Assignment If you are familiar with Perl, C, or Java, you might think that Bash would use commas to separate array elements,however this is not the case; …