Syntax (Linux in a Nutshell, 4th Edition)

Filename

Description

~/.tcshrc or ~/.cshrc

Executed at each instance of shell startup. If no ~/.tcshrc is found, tcsh uses ~/.cshrc if present.

~/.login

Executed by login shell after .tcshrc at login.

~/.cshdirs

Executed by login shell after .login.

~/.logout

Executed by login shell at logout.

/etc/passwd

Source of home directories for ~name abbreviations.

Characters

Meaning

Match any string of 0 or more characters.

Match any single character.

[abc...]

Match any one of the enclosed characters; a hyphen can be used to specify a range (e.g., a-z, A-Z, 0-9).

{abc,xxx,...}

Expand each comma-separated string inside braces.

Home directory for the current user.

~name

Home directory of user name.

% ls new* Match new and new.1 % cat ch? Match ch9 but not ch10 % vi [D-R]* Match files that begin with uppercase D through R % ls {ch,app}? Expand, then match ch1, ch2, app1, app2 % cd ~tom Change to tom's home directory

Characters

Description

;

Command separator

Background execution

( )

Command grouping

Pipe

* ? [ ] ~

Filename metacharacters

{ }

String expansion characters (usually don't require quoting)

> < & !

Redirection symbols

! ^

History substitution, quick substitution

" ' \

Used in quoting other characters

Command substitution

Variable substitution

newline space tab

Word separators

% echo 'Single quotes "protect" double quotes' Single quotes "protect" double quotes % echo "Well, isn't that "\""special?"\" Well, isn't that "special"? % echo "You have `ls|wc -l` files in `pwd`" You have 43 files in /home/bob % echo The value of \$x is $x The value of $x is 100

Command

Action

cmd &

Execute cmd in background.

cmd1 ; cmd2

Command sequence; execute multiple cmds on the same line.

(cmd1 ; cmd2)

Subshell; treat cmd1 and cmd2 as a command group.

cmd1 | cmd2

Pipe; use output from cmd1 as input to cmd2.

cmd1 `cmd2`

Command substitution; run cmd2 first and use its output as arguments to cmd1.

cmd1 || cmd2

OR; execute either cmd1 or (if cmd1 fails) cmd2.

cmd1 && cmd2

AND; execute cmd1 and then (if cmd1 succeeds) cmd2.

% cd; ls Execute sequentially % (date; who; pwd) > logfile All output is redirected % sort file | pr -3 | lp Sort file, page output, then print % vi `grep -l ifdef *.c` Edit files found by grep % egrep '(yes|no)' `cat list` Specify a list of files to search % grep XX file && lp file Print file if it contains the pattern % grep XX file || echo XX not found Echo an error message if XX not found

8.3.5. Redirection Forms

File descriptor	Name	Common abbreviation	Typical default
0	Standard input	stdin	Keyboard
1	Standard output	stdout	Screen
2	Standard error	stderr	Screen

The usual input source or output destination can be changed with redirection commands listed in the following sections.

8.3.5.1. Simple redirection

Command	Action
cmd > file	Send output of cmd to file (overwrite).
cmd >! file	Same as preceding, even if noclobber is set.
cmd >> file	Send output of cmd to file (append).
cmd>>! file	Same as preceding, even if noclobber is set.
cmd < file	Take input for cmd from file.
cmd << text	Read standard input up to a line identical to text (text can be stored in a shell variable). Input usually is typed on the screen or in the shell program. Commands that typically use this syntax include cat, echo, ex, and sed. If text is enclosed in quotes, standard input will not undergo variable substitution, command substitution, etc.

8.3.5.2. Multiple redirection

Command	Action
cmd >& file	Send both standard output and standard error to file.
cmd >&! file	Same as preceding, even if noclobber is set.
cmd >>& file	Append standard output and standard error to end of file.
cmd >>&! file	Same as preceding, even if noclobber is set.
cmd1 \|& cmd2	Pipe standard error together with standard output.
`(`cmd> f1) >& f2	Send standard output to file f1 and standard error to file f2.
cmd \| tee files	Send output of cmd to standard output (usually the screen) and to files. (See the example in Chapter 3 under tee.)

8.3.5.3. Examples

% cat part1 > book                       Copy part1 to book
% cat part2 part3 >> book                Append parts 2 and 3 to same file as part1
% mail tim < report                      Take input to message from report
% cc calc.c >& error_out                 Store all messages, including errors
% cc newcalc.c >&! error_out             Overwrite old file
% grep Unix ch* |& pr                    Pipe all messages, including errors
% (find / -print > filelist) >& no_access  Separate error messages from list of files
% sed 's/^/XX /' << "END_ARCHIVE"           Supply text right after command
This is often how a shell archive is "wrapped",
bundling text for distribution. You would normally
run sed from a shell program, not from the command line.
"END_ARCHIVE"

8.3. Syntax

8.3.1. Special Files

8.3.2. Filename Metacharacters

8.3.2.1. Examples

8.3.3. Quoting

8.3.3.1. Examples

8.3.4. Command Forms

8.3.4.1. Examples

8.3.5. Redirection Forms

8.3.5.1. Simple redirection

8.3.5.2. Multiple redirection

8.3.5.3. Examples