Bash reference

Essential commands

Knowledge of these commands is required to pass both the exercises and exam.

  • cat: show file contents on terminal
  • cd: change directory
    • cd ~: go to your home folder
    • cd ..: go to parent folder
  • chmod: change permissions
  • comm: compare two sorted files line by line
    • comm -12: only output lines common to both files
  • cp: copy file/folder
  • du: calculate file size
    • du -h: display file size in a human-readable format
  • echo: display a line of text
  • grep: find a regular expression in a text file
    • grep -E: use extended regular expressions
    • grep -v: invert sense of matching, select non-matching lines
    • grep -o: print only the matched part of a line
  • gunzip: expand a file that has been compressed in GZ format; replaces the zipped file with the uncompressed file
    • gunzip -c: write unzipped file contents to stdout (useful for piping)
  • head: output the first lines of a file (by default, the first 10 lines)
    • head -5 or head -n5: print the first 5 lines
  • less: display the contents of a file
  • ls: list directory contents
    • ls -l: use a long listing format, i.e., one file/folder per line with additional information (permissions, owner, size, date modified)
    • ls -a: show all files/folders (i.e., even those starting with .)
  • man: show the manual for a command
  • mkdir: create folder
    • mkdir -p: when creating nested folders, also create parent folders
  • mv: move file/folder
  • nano: edit a text file
  • passwd: change password
  • pwd: output the current working directory
  • sed: filter and transform text
    • sed 's/foo/bar/g': substitute all occurrences of foo with bar (details)
  • sort: sort lines in a text file
  • ssh user@host: connect to a server host with user user
  • tail: output the last lines of a file (by default, the last 10 lines)
    • tail -5 or tail -n5: print the last 5 lines
  • touch: change file timestamp; create empty file if it does not exist
  • uniq: omit repeated lines of text
  • wc: print newline, word, and byte counts for each file
    • wc -l: only print the number of lines
  • wget: download a file

Other commands

These commands are required for the exercises, but less important for the exam.

  • clear: clear the terminal
  • gzip: compress a file
  • md5sum: calculate the MD5 checksum of a file
  • source: run bash commands stored in a text file
  • tr: translate or delete characters
    • tr -d: delete character
  • zless: scroll through a zipped file

Important concepts

Special symbols

  • The ( is called a parenthesis
  • The [ is called a squared bracket (sometimes only bracket)
  • The { is called a curly bracket (sometimes only brace)
  • The ~ is called a tilde
  • The * is called an asterisk