Essential Unix/Linux terminal commands

Navigate

pwd                  # show the current directory
cd folder/           # move into "folder"
cd ..                # go up one level
cd -                 # back to the previous directory
ls -lah              # list (detail, hidden files, human-readable sizes)

Files and folders

touch file           # create an empty file (or bump its timestamp)
mkdir -p a/b/c       # create nested folders in a single command
cp file dest         # copy a file
cp -r src/ dst/      # copy a folder (recursive)
mv a b               # move or rename
rm file              # delete a file
rm -i file           # delete, asking for confirmation first
rm -r folder/        # delete a folder and everything in it

Search

find . -name "*.log" -mtime -1   # .log files modified less than a day ago
grep -rn "TODO" src/               # search "TODO" recursively, with line numbers
rg "pattern"                         # ripgrep: same idea, much faster

Read and filter

cat file                # print the whole file at once
less file               # page through it (q to quit)
head -n 20 file         # first 20 lines
tail -f app.log         # last lines, following new ones live
wc -l file              # count lines
sort file | uniq -c     # sort then count duplicates
cut -d',' -f1 data.csv  # extract the 1st column of a CSV file

Processes

ps aux               # list every running process
ps aux | grep node   # keep only processes containing "node"
top                  # real-time process monitor
htop                 # friendlier equivalent (needs installing separately)
kill -9 <pid>        # force-stop a process by its PID
command &            # run a command in the background
jobs                 # list the session's background jobs
fg                   # bring the last job to the foreground
bg                   # resume a paused job in the background

Permissions and quick redirections

chmod +x script.sh        # make it executable
sudo command                # run as administrator
command > file             # redirect output (overwrite)
command >> file            # redirect, appending to the end
command1 | command2        # chain: output of 1 = input of 2

Links and archives

ln -s /path/to/target link     # create a symbolic link
tar -czvf archive.tar.gz folder/    # compress (gzip)
tar -xzvf archive.tar.gz            # extract
zip -r archive.zip folder/          # compress into a zip
unzip archive.zip                   # extract a zip

Environment variables

echo $HOME               # show a variable
export MY_VAR="value"    # set it for the current session
env                       # list every variable
which command             # path to the executable being used

Disk space and network

df -h                    # disk space per partition
du -sh folder/           # total size of a folder
ping example.com         # test connectivity
curl -I https://example.com   # fetch just the HTTP headers