RHCSA Essential Command-Line Tools Flashcards

Which command displays the last 20 lines of a file named 'syslog'?

Answer: tail -20 syslog

The tail command with -N flag outputs the last N lines of a file.

What does the command 'wc -l filename' report?

Answer: Number of lines in the file

The wc -l option counts and displays the number of newline characters (lines) in a file.

Which command would you use to search for the string 'error' recursively in all files under /var/log?

Answer: grep -r 'error' /var/log

grep -r performs a recursive search through directories for a pattern.

What is the effect of running 'sort -u file.txt'?

Answer: Sorts the file and removes duplicate lines

The sort -u option sorts lines and suppresses duplicate output lines, keeping only unique entries.

Which sed command replaces only the FIRST occurrence of 'foo' with 'bar' on each line of input?

Answer: sed 's/foo/bar/' file

Without the g flag, sed's s command replaces only the first match on each line by default.

What does the 'cut -d: -f1' command do when applied to /etc/passwd?

Answer: Extracts the first field using colon as delimiter

cut -d: -f1 uses colon as the field delimiter and extracts field number 1, which is the username in /etc/passwd.

Which command can be used to view a file page by page, allowing both forward and backward navigation?

Answer: less

less allows forward and backward navigation through a file, unlike more which only scrolls forward.