10 Essential Unix Shell Hacks to Boost Your Productivity

1. File name completion

File name completion lets you avoid typing long paths manually. The method varies by shell, so first determine which shell you are using.

Determine your shell

echo $0 ps -p $$

C Shell enables completion via the filec variable (set with set filec) and the Esc key.

Bash provides Tab‑based completion by default; pressing Tab once shows the longest common prefix, pressing twice lists all matches.

Korn Shell uses the EDITOR variable: vi → Esc then \, emacs → double Esc.

2. History expansion

Reuse the previous command’s arguments with !$. For example, after searching a file with grep pickles this‑is‑a‑long‑lunch‑menu‑file.txt, you can edit the same file directly:

vi !$

3. Reusing earlier parameters

The !: operator selects specific arguments from the previous command. !:1 returns the first argument, which can be combined with !$ to manipulate files.

mv kxp12.c file_system_access.c ln -s !$ !:1

4. Managing directory navigation with pushd/popd

pushd

adds the current directory to a stack and switches to a new one; popd returns to the previous directory. dirs displays the stack.

pushd . pushd /etc pushd /var pushd /usr/local/bin dirs popd

You can rotate the stack with pushd +n or pushd -n.

5. Finding large files

Use df to check filesystem usage, then locate files larger than a threshold with find and the -size option (size is in kilobytes).

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

6. Creating temporary files without an editor

Redirect standard input to a file using cat > filename. Finish input with Ctrl‑D. To append instead of overwrite, use >>.

cat > my_temp_file.txt cat >> my_temp_file.txt

7. Using curl for data transfer

curl

retrieves data over many protocols (HTTP, FTP, etc.). Use -o to save the output to a file.

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

8. Effective regular‑expression usage

Regular expressions (regex) define patterns for matching text. Common constructs include ^ (start of line), $ (end of line), character classes [...], quantifiers *, and ranges {x,y}. They are frequently used with grep:

grep '^From: ' /usr/mail/$USER grep '[a-zA-Z]' search-file.txt grep '[^a-zA-Z0-9]' search-file.txt grep '[0-9]{3}-[0-9]{4}' search-file.txt

9. Determining the current user

Run whoami to display the effective username. It can be used in scripts to prevent execution as root:

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

10. Processing data with awk

awk

is a powerful text‑processing tool. Examples:

Print line length: awk '{ i = length($0); print i }' file Find position of a substring: awk '{ i = index($0,"ing"); print i }' file Tokenize a line:

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

Summarize CSV data: awk -F, '{print $1,$2+$3+$4}' sales Source: IBM developerWorks (https://www.ibm.com/developerworks/cn/aix/library/au-unixtips/).