Linux Administration Practice Exam

The ls command lists directory contents. Common flags:
-l long format with permissions, owner, size, date
-a show hidden files (dotfiles)
-h human-readable sizes
-R recursive listing
-t sort by modification time

grep searches text using patterns.
Usage: grep [options] pattern [file...]
Key flags:

• -i case-insensitive
• -r recursive search
• -n show line numbers
• -v invert match
• -E extended regex (same as egrep)

find searches the directory tree.
Examples:
find /home -name "*.txt" — find by name
find . -type f -mtime -7 — files modified in last 7 days
find / -size +100M — files larger than 100MB
find . -perm 755 — find by permissions
find . -name "*.log" -exec rm {} \; — execute command on results

awk is a powerful text-processing language that operates on fields and records.
Examples:
awk '{print $1, $3}' file — print columns 1 and 3
awk -F: '{print $1}' /etc/passwd — set delimiter to colon
awk '$3 > 100 {print $0}' data.txt — conditional filtering
Built-in variables: NR (record number), NF (number of fields), FS (field separator)

sed (stream editor) transforms text in a pipeline.
Common usage:
sed 's/old/new/' file — replace first occurrence per line
sed 's/old/new/g' file — replace all occurrences
sed -i 's/old/new/g' file — edit file in-place
sed -n '5,10p' file — print lines 5–10
sed '/pattern/d' file — delete matching lines