Linux command line
Preface
I would be fooling myself if I claim to be proficient in Linux command line. So I took the Linux Command Line video course to enhance my knowledge in the area.
ls: list directory content
Userful Options:
| Option | Meaning |
|---|---|
| -l | use a long listing format |
| -a | do not ignore entries starting with . |
| -h | with -l, print sizes in human readable format (e.g. 1K 234M 2G) |
whatis: displays short manual page descriptions
whatis cp
// output:
cp(1) - copy files
file: find the type of a file
file README.md
// output:
README.md: ASCII text
head: output the first part of file
Userful Options:
| Option | Meaning |
|---|---|
| -n | specify the number of first lines to print |
tail: output the last part of file
Userful Options:
| Option | Meaning |
|---|---|
| -n | specify the number of last lines to print |
| -f | loop forever, checking for new data at the end of the file(s) |
wildcard: a symbol used to replace or represent one or more characters.
| wildcard | Meaning |
|---|---|
| * | The asterisk in a wildcard matches any character zero or more times |
| ? | A question mark matches a single character once |
| [] | match a single character in a range |
touch chapters{1,2,3}.txt
// will create chapters1.txt, chapters2.txt and chapters3.txt
tar: create, maintain, modify, and extract files that are archived in the tar format.
Userful Options:
| Option | Meaning | Example |
|---|---|---|
| -c | create a new archive. | tar -cf archive.tar file1 file2 |
| -f | use archive file or device ARCHIVE | |
| -v | verbosely list files processed. | |
| -x | untar tar archive file | tar -cvf archive.tar |
gzip: compress
wget: download file over network.
Userful Options:
| Option | Meaning | Example |
|---|---|---|
| -O | specify output | wget -O file http://foo |
id: prints real and effective user and group ID
uid=501(michaelzheng) gid=20(staff) groups=20(staff),12(everyone)
groups: show group memberships
groups
//staff everyone
whoami: prints the effective user
whoami
//michaelzheng
chmod: change the permissions of files or directories
For a file with listing like this:
-rw-r--r-- 1 michaelzheng staff 1983 Jul 17 16:17 README.md
The first char is the type. The 2-4 is the owner permission for reading, writing and execution respectively. 5-6 is for group members and 9-11 is for others. Taking the example above for illustration:
- -: normal file
- rw-: owner(i.e. michaelzheng) can read and write
- r--: groups members can only read
- r--: others can only read
To change each permission group, we can convert binary representation to octal format.
| r | w | e |
|---|---|---|
| 4(i.e. 2^2) | 2(i.e. 2^1) | 1(i.e. 2^0) |
Therefore, if I want to grant owner rwx(4 * 1 + 2 * 1 + 1 * 1 = 7), group member rx(4 * 1 + 2 * 0 + 1 * 1 = 5) and others r (4 * 1 + 2 * 0 + 1 * 0 = 4) then i can use
chmod 750 README.md
ps: displays information about a selection of the active processes
jobs: display status of jobs in the current session
fg: run jobs in the foreground
bg: run jobs in the background
df: report file system usage
Useful options:
| Option | Meaning |
|---|---|
| -h | print sizes in human readable format |
du -h
//output:
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk1 112Gi 97Gi 15Gi 87% 2771640 4292195639 0% /
devfs 182Ki 182Ki 0Bi 100% 630 0 100% /dev
map -hosts 0Bi 0Bi 0Bi 100% 0 0 100% /net
map auto_home 0Bi 0Bi 0Bi 100% 0 0 100% /home
du: estimate file space usage
Useful options:
| Option | Meaning |
|---|---|
| -h | print sizes in human readable format |
| -s | display only a total for each argument |
Reference
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