10 Essential Unix Command-Line Tricks to Boost Your Productivity

File name completion

Identify the current shell with echo $0 or ps -p $$. In C shell enable completion by setting filec. Bash provides Tab‑based completion by default. In Korn shell the completion behavior depends on the EDITOR variable: vi mode uses Esc \, emacs mode uses Esc Esc.

History expansion

Reuse the last argument of the previous command with !$. Example: after grep pickles this‑is‑a‑long‑lunch‑menu‑file.txt, edit the same file with vi !$ without retyping the filename.

Reusing previous arguments

!$

returns the last argument, while !:1 returns the first argument of the previous command. Combining them allows actions such as renaming a file and creating a symbolic link to the original name:

mv kxp12.c file_system_access.c
ln -s !$ !:1   # creates link file_system_access.c -> kxp12.c

Directory stack with pushd and popd

pushd

changes the current directory and pushes it onto a stack; popd removes the top entry and returns to the previous location. dirs displays the stack. Example sequence:

pushd .
pushd /etc
pushd /var
pushd /usr/local/bin
dirs
popd
popd
# rotate stack
pushd +1   # move second entry to top
pushd -1   # move top entry down

Finding large files

Use df to view filesystem usage. To locate files larger than 10 MB:

find / -size +10000k -xdev -exec ls -lh {} \;

Creating temporary files without an editor

Redirect standard input with cat:

cat > my_temp_file.txt
This is my temp file text
^D
cat my_temp_file.txt   # displays the content

Append instead of overwrite using >>:

cat >> my_temp_file.txt
More text
^D

Using curl for web requests

Download a file via HTTP/HTTPS:

curl -o archive.tar http://www.somesite.com/archive.tar

See man curl for additional options.

Effective use of regular expressions

Common metacharacters:

^ – start of line

$ – end of line

\ – escape next character

[] – character class

[^] – negated class

. – any single character except newline

* – zero or more of the preceding element

{x,y} – between x and y repetitions

Examples with grep:

grep '^From: ' /usr/mail/$USER
grep '[0-9]{3}-[0-9]{4}' file   # phone numbers

Determining the current user

Run whoami to display the effective username. In scripts, prevent execution as root:

if [ "$(whoami)" = "root" ]; then
  echo "You cannot run this script as root."
  exit 1
fi

Processing data with awk

Print line length: awk '{ print length($0) }' file Find position of a substring (e.g., "ing"): awk '{ print index($0,"ing") }' file Tokenize a line into words:

awk '{ n=split($0,a," "); for(i=1;i<=n;i++) print a[i] }' file

Summarize CSV data (comma‑separated values): awk -F, '{ print $1, $2+$3+$4 }' sales The command prints each salesperson’s name followed by the total of the numeric fields.