Learn Enough Command Line

• 1 Basics
  • 1.1 Running a terminal
  • 1.2 Our first command
  • 1.3 Man pages
  • 1.4 Editing the line
  • 1.5 Cleaning up
  • 1.6 Summary
• 2 Manipulating files
  • 2.1 Redirecting and appending
  • 2.2 Listing
    • Hidden files
  • 2.3 Renaming, copying, deleting
    • Box 8. Tab completion
    • Unix terseness
  • 2.4 Summary
• 3 Inspecting files
  • 3.1 Downloading a file
    • Box 9. Repeating previous commands
  • 3.2 Making heads and tails of it
    • Wordcount and pipes
  • 3.3 Less is more
  • 3.4 Grepping
  • 3.5 Summary
• 4 Directories
  • 4.1 Directory structure
    • Box 11. “sudo make me a sandwich.”
  • 4.2 Making directories
  • 4.3 Navigating directories
    • Box 12. Combining commands
  • 4.4 Renaming, copying, and deleting directories
    • Grep redux
  • 4.5 Summary
• 5 Conclusion

1 Basics

Figure 2: A prototypical command-line command.

1.1 Running a terminal

Figure 5: Anatomy of a command line. (Your prompt may differ.)

Figure 7: A terminal window with three tabs.

Figure 8: Some menu items for the default macOS terminal.

keyboard shortcut: ⌃T

1.2 Our first command

$ echo hello
hello
$

double quotes, single quotes

$ echo "goodbye"
goodbye
$ echo 'goodbye'
goodbye
$

Listing 1: Printing “hello, goodbye” two different ways.

$ echo hello, goodbye
hello, goodbye
$ echo "hello, goodbye"
hello, goodbye
$

One thing that can happen when using quotes is accidentally not matching them, as follows:

$ echo "hello, goodbye
>

keyboard shortcut:
Ctrl-C Get out of trouble

Figure 9: This cat appears to be stuck and should probably hit Ctrl-C.

1.3 Man pages

Listing 2: The result of running man echo.

$ man echo

ECHO(1)                   BSD General Commands Manual                  ECHO(1)

NAME
     echo -- write arguments to the standard output

SYNOPSIS
     echo [-n] [string ...]

DESCRIPTION
     The echo utility writes any specified operands, separated by single blank
     (` ') characters and followed by a newline (`\n') character, to the stan-
     dard output.

     The following option is available:

     -n    Do not print the trailing newline character.  This may also be
           achieved by appending `\c' to the end of the string, as is done by
           iBCS2 compatible systems.  Note that this option as well as the
           effect of `\c' are implementation-defined in IEEE Std 1003.1-2001
           (``POSIX.1'') as amended by Cor. 1-2002.  Applications aiming for
           maximum portability are strongly encouraged to use printf(1) to
           suppress the newline character.
:

on any system you should be able to access subsequent information one line at a time by pressing the down arrow key, or one page at a time by pressing the spacebar. To exit the man page, press “q” (for “quit”).

Figure 10: Applying man to man.

Listing 3: The result of running man man.

$ man man

man(1)                                                                  man(1)

NAME
       man - format and display the on-line manual pages

SYNOPSIS
       man  [-acdfFhkKtwW]  [--path]  [-m system] [-p string] [-C config_file]
       [-M pathlist] [-P pager] [-B browser] [-H htmlpager] [-S  section_list]
       [section] name ...

DESCRIPTION
       man formats and displays the on-line manual pages.  If you specify sec-
       tion, man only looks in that section of the manual.  name  is  normally
       the  name of the manual page, which is typically the name of a command,
       function, or file.  However, if name contains  a  slash  (/)  then  man
       interprets  it  as a file specification, so that you can do man ./foo.5
       or even man /cd/foo/bar.1.gz.

       See below for a description of where man  looks  for  the  manual  page
       files.

OPTIONS
       -C  config_file
:

man [-acdfFhkKtwW] [--path] [-m system] [-p string] ...

Figure 11: “Tech Support Cheat Sheet” (via xkcd). See Box 5 for three extra techniques.

1.4 Editing the line

Key	Symbol
Command	⌘
Control	⌃
Shift	⇧
Option	⌥
Up, down, left, right	↑ ↓ ← →
Enter/Return	↵
Tab	⇥
Delete	⌫

Table 1: Miscellaneous keyboard symbols.

If you're using a keyboard made for Windows PCs, use the Alt key instead of Option, and the Windows logo key instead of Command.

keyboard shortcut:

• ⌃A Move to beginning of line
• ⌃E Move to end of line
• ⌃U Delete to beginning of line

1.5 Cleaning up

$ clear

keyboard shortcut: ⌃L

$ exit

keyboard shortcut: ⌃D

1.6 Summary

Command	Description	Example
echo <string>	Print string to screen	$ echo hello
man <command>	Display manual page for command	$ man echo
⌃C	Get out of trouble	$ tail ^C
⌃A	Move to beginning of line
⌃E	Move to end of line
⌃U	Delete to beginning of line
Option-click	Move cursor to location clicked
Up & down arrow	Scroll through previous commands
clear or ⌃L	Clear screen	$ clear
exit or ⌃D	Exit terminal	$ exit

Table 2: Important commands from Section 1.

2 Manipulating files

Figure 13: It’s not a bug, it’s a feature.

2.1 Redirecting and appending

$ echo "From fairest creatures we desire increase,"
From fairest creatures we desire increase,

redirect operator >:

$ echo "From fairest creatures we desire increase," > sonnet_1.txt

$ cat sonnet_1.txt
From fairest creatures we desire increase,

Figure 14: Viewing a file with cat.

append operator >>:

$ echo "That thereby beauty's Rose might never die," >> sonnet_1.txt

cat: “concatenate”

$ cat sonnet_1.txt
From fairest creatures we desire increase,
That thereby beauty's Rose might never die,

$ echo "From fairest creatures we desire increase," > sonnet_1_lower_case.txt
$ echo "That thereby beauty's rose might never die," >> sonnet_1_lower_case.txt

diff

$ diff sonnet_1.txt sonnet_1_lower_case.txt

2c2
< That thereby beauty's Rose might never die,
---
> That thereby beauty's rose might never die,

2.2 Listing

Listing 8: Listing files and directories with ls. (Output will vary.)

$ ls
Desktop
Downloads
sonnet_1.txt
sonnet_1_reversed.txt

Figure 15: The graphical equivalent of ls.

Listing 9: Running ls on a nonexistent file.

$ ls foo
ls: foo: No such file or directory
$ touch foo
$ ls foo
foo

wildcard character *:

$ ls *.txt
sonnet_1.txt
sonnet_1_reversed.txt

$ ls -l *.txt
total 16
-rw-r--r-- 1 mhartl staff  87 Jul 20 18:05 sonnet_1.txt
-rw-r--r-- 1 mhartl staff 294 Jul 21 12:09 sonnet_1_reversed.txt

ls -rtl: “list by reversed time of modification (long format)”

$ ls -rtl

Hidden files

ignore all files ending in “.txt”

$ echo "*.txt" > .gitignore
$ cat .gitignore
*.txt

$ ls
sonnet_1.txt
sonnet_1_reversed.txt

$ ls -a
.           .gitignore      sonnet_1_reversed.txt
..          sonnet_1.txt

2.3 Renaming, copying, deleting

rename a file
mv: “move”

$ echo "test text" > test
$ mv test test_file.txt
$ ls
test_file.txt

copy a file
cp: “copy”

$ cp test_file.txt second_test.txt
$ ls
second_test.txt
test_file.txt

deleting a file
rm: “remove”

$ rm -i second_test.txt
remove second_test.txt? y
$ ls second_test.txt
ls: second_test.txt: No such file or directory

Box 8. Tab completion

$ rm tes⇥

$ ls foo⇥

$ ls f⇥⇥

remove all the files ending with “.txt”
-f: “force”

$ rm -f *.txt

Unix terseness

instead of list, move, copy, and remove, we have ls, mv, cp, and rm.

Figure 16: The terseness of Unix commands can be a source of confusion.

2.4 Summary

Command	Description	Example
>	Redirect output to filename	$ echo foo > foo.txt
>>	Append output to filename	$ echo bar >> foo.txt
cat <file>	Print contents of file to screen	$ cat hello.txt
diff <f1> <f2>	Diff files 1 & 2	$ diff foo.txt bar.txt
ls	List directory or file	$ ls hello.txt
ls -l	List long form	$ ls -l hello.txt
ls -rtl	Long by reverse modification time	$ ls -rtl
ls -a	List all (including hidden)	$ ls -a
touch <file>	Create an empty file	$ touch foo
mv <old> <new>	Rename (move) from old to new	$ mv foo bar
cp <old> <new>	Copy old to new	$ cp foo bar
rm <file>	Remove (delete) file	$ rm foo
rm -f <file>	Force-remove file	$ rm -f bar

Table 3: Important commands from Section 2.

3 Inspecting files

3.1 Downloading a file

$ which curl
/usr/bin/curl

Listing 10: Using curl to download a longer file.

$ curl -OL cdn.learnenough.com/sonnets.txt
$ ls -rtl

Box 9. Repeating previous commands

exclamation point : !

$ echo "foo"
foo
$ !!
echo "foo"
foo

$ !curl

⌃R

$ <⌃R>

(reverse-i-search)`curl': curl -OL cdn.learnenough.com/sonnets.txt

3.2 Making heads and tails of it

head and tail

Listing 11: Looking at the head of the sample text file.

$ head sonnets.txt

Shake-speare's Sonnets

I

From fairest creatures we desire increase,
That thereby beauty's Rose might never die,
But as the riper should by time decease,
His tender heir might bear his memory:
But thou contracted to thine own bright eyes,
Feed'st thy light's flame with self-substantial fuel

Listing 12: Looking at the tail of the sample text file.

$ tail sonnets.txt

The fairest votary took up that fire
Which many legions of true hearts had warm'd;
And so the general of hot desire
Was, sleeping, by a virgin hand disarm'd.
This brand she quenched in a cool well by,
Which from Love's fire took heat perpetual,
Growing a bath and healthful remedy,
For men diseas'd; but I, my mistress' thrall,
 Came there for cure and this by that I prove,
 Love's fire heats water, water cools not love.

Wordcount and pipes

wc

$ wc sonnets.txt
    2620   17670   95635 sonnets.txt

lines, words, and bytes

Listing 13: Redirecting head and running wc on the result.

$ head sonnets.txt > sonnets_head.txt
$ wc sonnets_head.txt
      10      46     294 sonnets_head.txt

Listing 14: Piping the result of head through wc.

$ head sonnets.txt | wc
      10      46     294

3.3 Less is more

more , less

$ less sonnets.txt

Shake-speare's Sonnets

I

From fairest creatures we desire increase,
That thereby beauty's Rose might never die,
But as the riper should by time decease,
His tender heir might bear his memory:
But thou contracted to thine own bright eyes,
Feed'st thy light's flame with self-substantial fuel,
Making a famine where abundance lies,
Thy self thy foe, to thy sweet self too cruel:
Thou that art now the world's fresh ornament,
And only herald to the gaudy spring,
Within thine own bud buriest thy content,
And tender churl mak'st waste in niggarding:
  Pity the world, or else this glutton be,
  To eat the world's due, by the grave and thee.

II

When forty winters shall besiege thy brow,
And dig deep trenches in thy beauty's field,
sonnets.txt

Search file for string

Shake-speare's Sonnets

I

From fairest creatures we desire increase,
That thereby beauty's Rose might never die,
But as the riper should by time decease,
His tender heir might bear his memory:
But thou contracted to thine own bright eyes,
Feed'st thy light's flame with self-substantial fuel,
Making a famine where abundance lies,
Thy self thy foe, to thy sweet self too cruel:
Thou that art now the world's fresh ornament,
And only herald to the gaudy spring,
Within thine own bud buriest thy content,
And tender churl mak'st waste in niggarding:
  Pity the world, or else this glutton be,
  To eat the world's due, by the grave and thee.

II

When forty winters shall besiege thy brow,
And dig deep trenches in thy beauty's field,
/rose

Command	Description	Example
up & down arrow keys	Move up or down one line
spacebar	Move forward one page
⌃F	Move forward one page
⌃B	Move back one page
G	Move to end of file
1G	Move to beginning of file
/<string>	Search file for string	/rose
n	Move to next search result
N	Move to previous search result
q	Quit less

Table 4: The most important less commands.

3.4 Grepping

Listing 16: Finding the occurrences of “rose” in Shakespeare’s sonnets.

$ grep rose sonnets.txt

The rose looks fair, but fairer we it deem
As the perfumed tincture of the roses.
Die to themselves. Sweet roses do not so;
Roses of shadow, since his rose is true?
Which, like a canker in the fragrant rose,
Nor praise the deep vermilion in the rose;
The roses fearfully on thorns did stand,
  Save thou, my rose, in it thou art my all.
I have seen roses damask'd, red and white,
But no such roses see I in her cheeks;

Listing 17: Piping the results of grep to wc.

$ grep rose sonnets.txt | wc
      10      82     419

case-insensitive matching

• Type man grep
• Type /case and then return
• Read off the result (Figure 19)

Figure 19: The result of searching man grep for “case”.

3.5 Summary

Command	Description	Example
curl	Interact with URLs	$ curl -O example.com
which	Locate a program on the path	$ which curl
head <file>	Display first part of file	$ head foo
tail <file>	Display last part of file	$ tail bar
wc <file>	Count lines, words, bytes	$ wc foo
cmd1 | cmd2	Pipe cmd1 to cmd2	$ head foo | wc
ping <url>	Ping a server URL	$ ping google.com
less <file>	View file contents interactively	$ less foo
grep <string> <file>	Find string in file	$ grep foo bar.txt
grep -i <string> <file>	Find case-insensitively	$ grep -i foo bar.txt
ps	Show processes	$ ps aux
top	Show processes (sorted)	$ top
kill -<level> <pid>	Kill a process	$ kill -15 24601
pkill -<level> -f <name>	Kill matching processes	$ pkill -15 -f spring

Table 5: Important commands from Section 3.

4 Directories

4.1 Directory structure

$ ls /Users/mhartl/ruby

$ ls /usr/local/bin

Figure 20: The correspondence between folders & directories.

Box 11. “sudo make me a sandwich.”

$ touch /opt/foo
touch: /opt/foo: Permission denied

$ sudo touch /opt/foo
Password:

$ ls -l /opt/foo
-rw-r--r--  1 root  wheel  0  3 14 00:21 /opt/foo

$ rm -f /opt/foo
rm: /opt/foo: Permission denied
$ sudo !!
sudo rm -f /opt/foo
$ !ls
ls -l /opt/foo
ls: /opt/foo: No such file or directory

4.2 Making directories

mkdir : “make directory”

$ mkdir text_files

$ mv *.txt text_files/

$ ls text_files/
sonnet_1.txt     sonnet_1_reversed.txt sonnets.txt

$ ls -d text_files/
text_files/

ls -ld text_files/
drwxr-xr-x  4 wuyong  staff  136  3 14 00:50 text_files/

$ cd text_files/

cd tex⇥

pwd: “print working directory”

$ pwd
/Users/mhartl/text_files
$ ls
sonnet_1.txt     sonnet_1_reversed.txt sonnets.txt

4.3 Navigating directories

$ pwd
/Users/mhartl/text_files
$ cd ..
$ pwd
/Users/mhartl

Change to home directory

$ cd

$ cd ~

$ pwd
/Users/mhartl
$ mkdir second_directory
$ cd second_directory/

$ pwd
/Users/mhartl/second_directory
$ cd ~/text_files
$ pwd
/Users/mhartl/text_files

moving or copying files to the current directory:

$ pwd
/Users/mhartl/text_files
$ cd ~/second_directory
$ ls
$ cp ~/text_files/sonnets.txt .
$ ls
sonnets.txt

., find

$ cd
$ find . -name '*.txt'
./text_files/sonnet_1.txt
./text_files/sonnet_1_reversed.txt
./text_files/sonnets.txt

Perhaps my favorite use of . is in “open dot”, which will work only on macOS:

$ cd ~/ruby/projects
$ open .

to the previous directory

$ pwd
/Users/mhartl/second_directory
$ cd ~/text_files
$ pwd
/Users/mhartl/text_files
$ cd -
/Users/mhartl/second_directory

Box 12. Combining commands

$ ./configure ; make ; make install

$ ./configure && make && make install

The difference is that commands separated by && run only if the previous command succeeded. In contrast, with ; all the commands will be run no matter what, which will cause an error in the likely case that subsequent commands depend on the results of the ones that precede them.

4.4 Renaming, copying, and deleting directories

$ mkdir foo
$ mv foo/ bar/
$ cd foo/
-bash: cd: foo: No such file or directory
$ cd bar/

$ cd
$ mv bar foo
$ cd foo/

Listing 19: Copying a directory.

$ cd
$ mkdir foobar
$ cd foobar/
$ cp -r ../text_files .
$ ls
text_files

Listing 20: Copying with a trailing slash.

$ cp -r ../text_files/ .
$ ls
sonnet_1.txt     sonnet_1_reversed.txt sonnets.txt   text_files

$ cp ../text_files/* .

rmdir

$ cd
$ rmdir second_directory
rmdir: second_directory/: Directory not empty

rm -rf: “remove recursive force”

$ rm -rf second_directory/
$ ls second_directory
ls: second_directory: No such file or directory

Figure 22: This superhero understands how to use the power of rm -rf responsibly.

Grep redux

$ cd text_files/
$ mkdir foo
$ cd foo/
$ echo sesquipedalian > long_word.txt
$ cd

$ grep sesquipedalian text_files
grep: text_files: Is a directory

$ grep -r sesquipedalian text_files
text_files/foo/long_word.txt:sesquipedalian

$ grep -ri sesquipedalian text_files
text_files/foo/long_word.txt:sesquipedalian

4.5 Summary

Command	Description	Example
mkdir <name>	Make directory with name	$ mkdir foo
pwd	Print working directory	$ pwd
cd <dir>	Change to	$ cd foo/
cd ~/<dir>	cd relative to home	$ cd ~/foo/
cd	Change to home directory	$ cd
cd -	Change to previous directory	$ cd && pwd && cd -
.	The current directory	$ cp ~/foo.txt .
..	One directory up	$ cd ..
find	Find files & directories	$ find . -name foo*.*
cp -r <old> <new>	Copy recursively	$ cp -r ~/foo .
rmdir <dir>	Remove (empty) dir	$ rmdir foo/
rm -rf <dir>	Remove dir & contents	$ rm -rf foo/
grep -ri <string> <dir>	Grep recursively (case-insensitive)	$ grep -ri foo bar/

Table 6: Important commands from Section 4.

5 Conclusion