Shell Scripting & Automation Flashcards

Which cron field position specifies the day of the week?

Answer: Fifth field (0-7, where 0 and 7 = Sunday)

In a standard crontab, the five fields are minute, hour, day-of-month, month, day-of-week; the fifth field is day-of-week where both 0 and 7 represent Sunday.

What does `awk '{print $NF}' file` print?

Answer: The last field of each line

`NF` is the built-in awk variable for the number of fields, so `$NF` refers to the last field.

Which sed command deletes lines 3 through 7 from a file's output?

Answer: sed '3,7d' file

In sed, address ranges use a comma to separate start and end line numbers, followed by the command letter.

What is the effect of `chmod +x script.sh` on a script that has no execute bit set?

Answer: Adds execute permission for owner, group, and others

Using `+x` without specifying a user class adds execute permission to all three classes: user, group, and other.

Which bash substitution removes the longest matching suffix pattern from a variable?

Answer: ${var%%pattern}

`%%` removes the longest match of the pattern from the end (suffix), while `%` removes the shortest match.

How does `xargs -I {}` differ from plain `xargs` when constructing commands?

Answer: It places each argument at the {} placeholder position instead of appending at the end

`-I {}` defines a replace-string so each input item replaces `{}` wherever it appears in the command template.

What does `2>/dev/null` accomplish in a shell command?

Answer: Discards all error messages

Redirecting file descriptor 2 (stderr) to `/dev/null` silently discards all error output.