CS469/569 - Linux and Unix Administration and Networking Spring 2022

Common scripting utilities and programs:

> true

• Always succeeds (true)

> false

• Always fails (false)

> sort [-k n [ ,m ]] [ -n ] [ -r ] [ -u ] [ file ]

• Sort the lines in a file.
  -n - Numeric sort
  -r - Reverse order
  -u - Output only the unique entries
  -k n[,m] - Select field or fields to sort on.

> uniq [ -c ]

• Filters out adjacent matching lines.
  -c - Print a count

  Example:

  users | tr ' ' '\n' | uniq -c

  • outputs # number of unique users on a system.

> basename name [ suffix ]

• Strip the directory name [and suffix] from a filename.

> dirname name

• Strip last component from filename.

basename / dirname examples:

file="/some/path/to/file.txt";
dir=$(dirname "$file");                     # dir <- "/some/path/to"
filename=$(basename "$file");               # filename <- "file.txt"
basefilename=$(basename "$file" ".txt");    # basefilename <- "file"

> tr [ -d ] set1 [ set2 ]

• Translate or delete characters
  -d - Delete any characters in set1 from the input
• Otherwise translate set1 onto set2

> tac

• Cat files in reverse

> colrm [ first [ last ]]

• Remove (character) columns from a file.
  ex:
  ps aux | grep -v root | colrm 16 60

> cut [ -f field-number(s) ] [ -d deliminator-character ]

• Remove sections from each line of a file.
  ex:
  cut -f 1 -d : /etc/passwd

> tee

• Read from stdin and write to stdout and files at the same time.
  ex:
  ps aux | tee ps.out
  • Displays the output of ps aux while saving it to ps.out at the same time.

> env

• Run a program in a modified environment.
  ex:
  env -i PATH=/bin HOME=/tmp printenv

> date [-d when] [+format ]

• Print or set system date and time.
  Examples:

time=$(date +%s);

• Get the time in seconds since the epoch

date -d yesterday

• Yesterdays date

date -d '2021-03-01 yesterday'

• Last day of February 2021