unix.md

Unix

Command-Line Keystrokes

Keystroke	Action
CTRL-B	Move the cursor left
CTRL-F	Move the cursor right
CTRL-P	View the previous command (or move the cursor up)
CTRL-N	View the next command (or move the cursor down)
CTRL-A	Move the cursor to the beginning of the line
CTRL-E	Move the cursor to the end of the line
CTRL-W	Erase the preceding word
CTRL-U	Erase from cursor to beginning of line
CTRL-K	Erase from cursor to end of line
CTRL-Y	Paste erased text (for example, from CTRL-U)

Standard Error

You can redirect stderr

$ ls /fffff > file 2> error_file

The number 2 specifies the stream ID that the shell modifies. Stream ID 1 is standard output (the default), and 2 is standard error.

Redirect to the same file

$ ls /fffff > file 2>&1

Newer shortcut to 2>&1 in bash

$ ls -l /bin/usr &> ls-output.txt
$ ls -l /bin/usr &>> ls-output.txt

Standard Input Redirection

To channel a file to a program's standard input, use the < operator:

$ head < /proc/cpuinfo

head

Get n lines from the beginning of a file

head -n [int]

tail

Get n lines from the bottom of a file

tail -n [int]

Stream contents of a file

With --follow (-f), tail defaults to following the file descriptor, which means that even if a tail'ed file is renamed, tail will continue to track its end. This default behavior is not desirable when you really want to track the actual name of the file, not the file descriptor (e.g., log rotation). Use --follow=name in that case. That causes tail to track the named file in a way that accommodates renaming, removal and creation.

tail -f [file]

-F same as --follow=name --retry. Ideally used when you want to track/retry the actual name of the file, not the file descriptor (e.g., log rotation)

tail -F [file]

grep

Get line which contains search characters and n lines associated with search line

grep -C [int] [search]

cat

Get number of lines of text in all files in a given directory

cat $(find . -type f -print) | wc -l