test Command on Linux | Bash File Checks

test on Linux (and its [ ] alias) is how Bash scripts branch on files, permissions, and string length. Search volume is huge because every deploy script needs “if config exists, then …”.

File and directory tests

Classic single-bracket tests used in POSIX shells.

bashfiles

if [ -f /etc/nginx/nginx.conf ]; then echo "found"; fi
[ -d /var/www/html ] && echo "docroot exists"

Permissions

-r readable, -w writable, -x executable.

bashexecutable

[ -x /usr/local/bin/backup.sh ] || { echo missing; exit 1; }

Strings and integers

-z empty; use -eq for numbers, not == in old sh.

bashstrings

count=0
[ -z "$count" ] && echo empty
[ "$count" -eq 0 ] && echo zero

Prefer [[ ]] in Bash

Double brackets handle quoting and pattern matching more safely.

WarningAlways quote variables in [ ]: [ -n "$var" ] avoids word-split surprises.

Quick Reference

File: [ -f path ]
Dir: [ -d path ]
Use [[ ... ]] in Bash scripts when possible

test Command on Linux: Check Files, Strings and Integers in Bash