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export variable: export var set --export var Options discoverable via tab completion function-local variable: local var by default scope-local variable: no equivalent set --local var remove variable: unset var set --erase var check if a variable exists: test -v var set --query var array initialization: var=( a b c )
Also, positional parameters as the argv array including argv[1], the $0 shell variable as argv[0], the Count of Indices parameter expansion $#var, the -d and -x operators of a testing syntax regarding directory and executability tests, respectively, the ! negate symbol, a looping construct in the foreach command, the set, echo and exit commands ...
Variable completion is the completion of the name of a variable name (environment variable or shell variable). Bash, zsh, and fish have completion for all variable names. PowerShell has completions for environment variable names, shell variable names and — from within user-defined functions — parameter names.
VARIABLE=value # (there must be no spaces around the equals sign) export VARIABLE # for Bourne and related shells export VARIABLE=value # for ksh, bash, and related shells setenv VARIABLE value # for csh and related shells A few simple principles govern how environment variables achieve their effect.
The command supports several options via flags. It can be configured to issue a message using -p instead of needing to use the echo command. It can also superficially hide text using the -s flag, limit the amount of characters with -n, store the result in an array with -a, and timeout after a certain amount of time with -t.
It combines features from both ksh and tcsh, offering functionality such as programmable command-line completion, extended file globbing, improved variable/array handling, and themeable prompts. Zsh is available for Microsoft Windows as part of the UnxUtils collection and has been adopted as the default shell for macOS and Kali Linux. The "Oh ...
Many modern shells also supply various features usually found only in more sophisticated general-purpose programming languages, such as control-flow constructs, variables, comments, arrays, subroutines and so on. With these sorts of features available, it is possible to write reasonably sophisticated applications as shell scripts.
An array data structure can be mathematically modeled as an abstract data structure (an abstract array) with two operations get(A, I): the data stored in the element of the array A whose indices are the integer tuple I. set(A, I, V): the array that results by setting the value of that element to V. These operations are required to satisfy the ...