Text Processing and File OperationsLesson 4.4

Bash file and directory operations at scale

find command, find with exec, xargs for bulk operations, mktemp, file locking with flock, recursive operations, handling special filenames, stat command, file permissions with chmod

find: The Right Tool for File Operations

find searches a directory tree with precise criteria. Combine with -exec or xargs to act on results.

# Find all .log files modified in the last 7 days
find /var/log -name "*.log" -mtime -7

# Find and delete empty files
find /tmp -type f -empty -delete

# Execute a command per file
find . -name "*.sh" -exec chmod +x {} \;

# xargs: faster for large result sets
find . -name "*.log" | xargs gzip

# Handle filenames with spaces — use null delimiter
find . -name "*.txt" -print0 | xargs -0 wc -l

Safe Temp Files

tmpfile=$(mktemp)           # /tmp/tmp.XXXXXXXX
tmpdir=$(mktemp -d)         # creates a temp directory
trap "rm -rf $tmpfile $tmpdir" EXIT

echo "data" > "$tmpfile"
process_file "$tmpfile"

File Locking

#!/usr/bin/env bash
lockfile="/var/run/myscript.lock"

exec 9>"$lockfile"
if ! flock -n 9; then
  echo "Another instance is running" >&2
  exit 1
fi

echo "Got the lock. Running exclusively."
# Lock released automatically when script exits

Never use if [ -f lockfile ] for locking — it has a race condition. flock is atomic at the OS level.