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5.2. Syntax
This section describes the many symbols peculiar to the C shell. The topics are arranged as follows:
Special files
Filename metacharacters
Quoting
Command forms
Redirection forms
5.2.1. Special Files
| ~/.cshrc | Executed at each instance of shell invocation. |
| ~/.login | Executed by login shell after .cshrc at login. |
| ~/.logout | Executed by login shell at logout. |
| ~/.history | History list saved from previous login. |
| /etc/passwd | Source of home directories for ~name abbreviations. (May come from NIS or NIS+ instead.) |
5.2.2. Filename Metacharacters
| Metacharacter | Description |
|---|---|
| * | Match any string of zero 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. The strings need not match actual filenames. |
| ~ | Home directory for the current user. |
| ~name | Home directory of user name. |
5.2.2.1. Examples
% 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 % mv info{,.old} Expands to mv info info.old % cd ~tom Change to tom's home directory
5.2.3. Quoting
Quoting disables a character's special meaning and allows it to be used literally, as itself. The characters in the following table have special meaning to the C shell.
These characters can be used for quoting:
- " "
- Everything between " and " is
taken literally, except for
the following characters that keep their special meaning:
- $
- Variable substitution will occur.
- ‘
- Command substitution will occur.
- "
- This marks the end of the double quote.
- \
- Escape next character.
- !
- The history character.
- newline
- The newline character.
- ' '
- Everything between ' and ' is taken literally except for ! (history) and another ', and newline.
- \
- The character following a \ is taken literally. Use within "" to escape ", $, ‘, and newline. Use within '' to escape newlines. Often used to escape itself, spaces, or newlines. Always needed to escape a history character (usually !).
5.2.3.1. Examples
% echo 'Single quotes "protect" double quotes' Single quotes "protect" double quotes % echo "Don't double quotes protect single quotes too?" Don't double quotes protect single quotes too? % 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
5.2.4. Command Forms
| cmd & | Execute cmd in background. |
| cmd1 ; cmd2 | Command sequence; execute multiple cmd s 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; use cmd2 output as arguments to cmd1. |
| cmd1 && cmd2 | AND; execute cmd1 and then (if cmd1 succeeds) cmd2. This is a “short-circuit” operation; cmd2 is never executed if cmd1 fails. |
| cmd1 || cmd2 | OR; execute either cmd1 or (if cmd1 fails) cmd2. This is a “short-circuit” operation; cmd2 is never executed if cmd1 succeeds. |
5.2.4.1. Examples
% nroff file > file.out & Format in the background % 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 otherwise, echo an error message
5.2.5. Redirection Forms
| File Desciptor | Name | Common Abbreviation | Typical Default |
|---|---|---|---|
| 0 | Standard input | stdin | Keyboard |
| 1 | Standard output | stdout | Terminal |
| 2 | Standard error | stderr | Terminal |
The usual input source or output destination can be changed, as seen in the following sections.
5.2.5.1. Simple redirection
- cmd > file
- Send output of cmd to file (overwrite).
- cmd >! file
- Same as above, even if noclobber is set.
- cmd >> file
- Send output of cmd to file (append).
- cmd >>! file
- Same as above, but write to file 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 is usually typed at the terminal or in the shell program. Commands that typically use this syntax include cat, echo, ex, and sed. If text is quoted (using any of the shell-quoting mechanisms), the input is passed through verbatim.
5.2.5.2. Multiple redirection
| cmd >& file | Send both standard output and standard error to file. |
| cmd >&! file | Same as above, even if noclobber is set. |
| cmd >>& file | Append standard output and standard error to end of file. |
| cmd >>&! file | Same as above, but append to or create file even if noclobber is set. |
| cmd1 |& cmd2 | Pipe standard error together with standard output. |
| (cmd > f1) >& f2 | Send standard output to file f1, standard error to file f2. |
| cmd | tee files | Send output of cmd to standard output (usually the terminal) and to files. (See the Example in Chapter 2, under tee.) |
5.2.5.3. Examples
% cat part1 > book % cat part2 part3 >> book % mail tim < report % cc calc.c >& error_out % cc newcalc.c >&! error_out % grep Unix ch* |& pr % (find / -print > filelist) >& no_access % sed 's/^/XX /g' << "END_ARCHIVE" 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" XX This is often how a shell archive is "wrapped", XX bundling text for distribution. You would normally XX run sed from a shell program, not from the command line.
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| 5. The C Shell |  | 5.3. Variables |
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