bash

20 pages

• bash parse arguments with getopts and $@

  Parse command-line arguments in bash scripts using getopts for flags, positional parameters ($1, $2), and shift for more control.

• bash arrays — create, iterate, append, slice

  Create and use bash arrays: declare, iterate with for, append elements, get length, slice, and use associative arrays.

• bash check exit code of last command — $?

  Check the exit code of the last bash command with $?. Exit code 0 means success; anything else means failure.

• bash check if file or directory exists

  Test if a file, directory, or symlink exists in bash using [ -f ], [ -d ], [ -e ], and [ -L ] in an if statement or inline.

• bash: command not found — how to fix

  Fix "bash: command not found" by checking PATH, installing the missing program, or using the full path to the binary.

• crontab syntax and common schedules

  Crontab syntax reference with common schedule examples. Covers the five time fields, special strings (@daily, @reboot), and editing cron jobs.

• bash date — format date and timestamp

  Format dates and timestamps in bash using the date command. Covers ISO 8601, Unix epoch, arithmetic, and macOS vs Linux differences.

• bash find files by name, extension, or age

  Use the find command to locate files by name, extension, size, modification date, or content. Includes -exec, -mtime, and -type options.

• bash for loop — iterate over files, list, range

  Use bash for loops to iterate over files, lists, arrays, ranges, and command output. Covers glob patterns, C-style loops, and while loops.

• bash heredoc — write multiline strings

  Use heredoc (<<EOF) to embed multiline text in bash scripts. Covers indented heredocs (<<-), variable expansion, and writing to files.

• bash kill process by port number

  Kill the process listening on a specific port using lsof, fuser, or ss. Works on Linux and macOS.

• bash: no such file or directory — how to fix

  Fix "bash: no such file or directory" caused by wrong path, missing file, Windows line endings (CRLF), or a missing interpreter.

• bash permission denied — how to fix (chmod +x)

  Fix "bash: ./script.sh: Permission denied" by adding execute permission with chmod +x. Covers common permission issues and setuid.

• bash set -o pipefail — catch errors in pipelines

  Use set -o pipefail to make bash pipelines fail when any command in the pipeline fails, not just the last one.

• bash read a file line by line

  Read a file line by line in bash using a while read loop. Handles lines with spaces, special characters, and trailing newlines correctly.

• bash redirect stderr to stdout — 2>&1 and &>

  Redirect stderr (2) to stdout (1) in bash using 2>&1. Includes capturing both streams, redirecting to a file, and suppressing output.

• bash set -e — exit script on error

  Use set -e (errexit) to make a bash script exit immediately when any command fails. Covers caveats, set -u, and set -o pipefail.

• bash string comparison — equality, contains, starts with

  Compare strings in bash using [[ ]] with =, !=, =~, and parameter expansion. Covers equality, contains, starts with, ends with, and empty checks.

• bash syntax error: unexpected end of file — how to fix

  Fix "syntax error: unexpected end of file" in bash scripts caused by unclosed if/for/while, missing fi/done/esac, or CRLF line endings.

• bash xargs — run a command for each input line

  Use xargs to pass stdin lines as arguments to a command. Covers -I, -P for parallel execution, null-delimited input, and safe filenames with spaces.