Bash: Useful Commands¶
Bash is a widely shell, which is the default shell in many operating systems, e.g. Unix, Linux, Mac OS. Bash can help you achieve a lot. To invest time to learn some useful commands in bash is a good idea.
Contents
Directory commands¶
Home directory¶
For every user, there is a home directory which is presented by ~
cd will go to home directory
Wildcard¶
Bash supports wild card to match files.
*
Matches anything, including nothing at all
?
Matches exactly 1 character
[acd7_]
Matches one of the characters in the list, above example would match a, c, d, 7 or _
Another example is: [^ax2] matches anything but a, x, 2
You can also use ranges, e.g. [a-z], [0-9], [A-C3-5]
Brace Expansion¶
Brace expansion is another handy way for you to write compact commands.
touch {a,b,c}.txt => touch a.txt b.txt c.txt
mv file.{txt,jpg} dir/ => mv file.txt file.jpg dir
touch {a..c}{1..3}.txt => touch a1.txt a2.txt ... c2.txt c3.txt
mv *{txt,jpg} Documents => mv *txt *jpg Documents
File Manipulation¶
Input/Output redirection¶
Output redirection is very important tool, which has two modes:
> will overwrite
>> will append
< is input redirect
Modify file¶
Touch will create a empty file or update access time on an existing file
sort command can sort the content in the file.
sort -nk2 [filename]*: can sort the content of file according to the second column
tr can replace character
tr 'Hello' 'hello' < test > test2
cut: cut out selected positions of each line of a file
cut -c2 test => cut the second character of each line in test file
paste: get content from various files and put into one file
paste test test2
join: do the similar thing like paste but get rid of the header for each row
Search file¶
grep command will do the search and list all the relevant lines
grep -nr security . => search keyword security in current folder
find can use pattern to find files
find . -name "*.rst" => find all rst files under current folder
wc: count lines, words and characters in a file
uniq: do not show duplicated items
head and tail: show the beginning and end of the file
View help and file content¶
Use man to see the help manual
Space: down the page
B: up the page
/: search. N, n to go to next/previous match
Q: exit
Use less command to view a file, use the same keys like man
Process¶
If you start a long process by a normal way, the terminal will be blocked.
Ctrl + Z will pause the process.
fg will bring back the process.
bg will let the process run in the background
When you start a long program, you can also ends up a &, which means run in background
jobs: see the process in background
kill can kill a process. e.g. kill %1
ps -e: list processes
The difference between jobs and ps is jobs only list the process managed by the shell.
Other tips¶
Commands parameters¶
The command option can be combined in one dash
For example: ls -l -a
Can be: ls -la
Avoid keeping sudo¶
In some operating system, if your account is not admin you will be asked to type sudo often. It is inconvenient.
sudo -s: can avoid typing sudo every time
Shortcut keys¶
Ctrl-a: Start of line
Ctrl-e: End of line
Ctrl-Left: Forward 1 word
Ctrl_Right: Back 1 word
Alt-D: Delete a word
Alt-Backspace: Delete a word backward
Ctrl-K: Delete rest of line
Ctrl-U: Delete from start of line
Ctrl-R: Search back in history
