When should I use cut instead of awk?

Q: When should I use cut instead of awk?

cut is fine for picking fields when the delimiter is a single fixed character, like : here. It cannot filter rows, compare values, or handle runs of spaces as one separator. For whitespace-aligned output such as ps or df, use awk, whose default separator treats any run of spaces or tabs as one.

Bash and Linux

List users whose login shell is bash

easyawk and cut Must-do

During a server hardening review you need the accounts that can get an interactive bash shell. /etc/passwd has seven colon-separated fields, and the seventh is the login shell. Print the username (field 1) of every account whose shell is exactly /bin/bash.

passwd

TEXT

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
deploy:x:1001:1001:Deploy User:/home/deploy:/bin/bash
postgres:x:112:120:PostgreSQL administrator:/var/lib/postgresql:/bin/bash
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync

Examples

Example 1

Input: Run the command on `passwd` (use `/etc/passwd` on a real host).

Output: root deploy postgres

Hints

Approach

-F: tells awk to split each line on colons, so $1 is the username and $7 the shell. The pattern $7 == "/bin/bash" is an exact string comparison on the shell field only, so a home directory or comment that happens to contain /bin/bash cannot cause a false match. The action {print $1} runs only for lines where the pattern is true. The awk program is in single quotes so the shell does not expand $7 and $1.

Bash

awk -F: '$7 == "/bin/bash" {print $1}' passwd

Follow-up questions

How would you list every account that can log in at all, i.e. whose shell is not nologin or false?
On a host using LDAP, why might /etc/passwd be incomplete? (getent passwd)

Frequently asked questions

cut is fine for picking fields when the delimiter is a single fixed character, like : here. It cannot filter rows, compare values, or handle runs of spaces as one separator. For whitespace-aligned output such as ps or df, use awk, whose default separator treats any run of spaces or tabs as one.