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Bash Quick Reference

#linux#bash

Intro

This is a reference post for Bash commands and utilities I have used. The official Bash manual is the definitive resource for anything more in-depth.

Timing a Script

The time builtin measures how long a command or script takes to run. It works for any executable, not just shell scripts.

time yourscript.sh

It also works for Python scripts or any other command:

time python script.py

This outputs three time values:

  • Real — Wall clock time from start to finish. Includes time spent waiting on I/O, time slices used by other processes, and any blocking.
  • User — CPU time spent in user-mode code (outside the kernel). Only counts actual CPU cycles consumed by the process itself.
  • Sys — CPU time spent inside the kernel on behalf of the process (system calls). Does not include user-space library code.

Generating Random Strings

Two quick options for generating random strings — useful for secrets, tokens, or temporary identifiers.

Using $RANDOM piped through md5sum (produces a 20-character hex string):

echo $RANDOM | md5sum | head -c 20; echo

Using openssl for a cryptographically secure base64-encoded string:

openssl rand -base64 32

For more options and approaches, see this reference.

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