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| # | anything following a # to the end of the current line is treated as a comment and ignored. If the first character of a script file is #, a C shell is invoked. Otherwise a Bourne shell is invoked. |
| #!interpreter | if the first line of a script file starts with this, then the script is run by the specified interpreter. For example, #!/bin/ksh would cause a Korn shell to be invoked. C shell options flags can also be enabled here. |
The C shell provides a number of options that are useful in debugging scripts: –n, –v, and –x (see C Shell Options). The –n option causes commands to be read without being executed and is used to check for syntax errors. The –v option causes the input to displayed as it is read. The –x option causes commands in C shell scripts to be displayed as they are executed. This is the most useful, general debugging option. For example, tscript could be run in trace mode if invoked “csh –x tscript”.
| ~/.cshrc | read at beginning of execution by C shell |
| ~/.history | contains previously executed commands |
| ~/.login | read by login shell after .cshrc file |
| ~/.logout | read by login shell at logout |
Regular expressions are used in many UNIX commands, including awk, ed, egrep, grep, sed, and vi.
| c | non-special character c | ||||||||||
| \c | special character c | ||||||||||
| ^ | beginning of line | ||||||||||
| $ | end of line | ||||||||||
| . | any single character | ||||||||||
| [abc] | any character a, b, or c | ||||||||||
| [a–c] | any character in range a through c | ||||||||||
| [^abc] | any character except a, b, or c | ||||||||||
| [^a–c] | any character except characters in range a through c | ||||||||||
| \n | nth \(...\) match (grep only) | ||||||||||
| rexp* | zero or more occurrences of regular expression rexp
| rexp+
| one or more occurrences of regular expression rexp
| rexp?
| zero or one occurrence of regular expression rexp
| rexp1 | rexp2
| regular expressions rexp1 or rexp2
| \(rexp\)
| tagged regular expression rexp (grep only)
| (rexp)
| regular expression rexp (egrep only)
| |
The following commands are frequently used in C shell scripts to filter input and output.
awk/nawk - Pattern Scanning and Processing Language
$awk [ options ] [ 'program' ] [ parameters ] [ files ] $nawk [ options ] [ 'program' ] [ files ]
Description:
The awk/nawk command performs actions for lines in files that match patterns specified in program. Each input line is made up of fields separated by whitespace.
Options:
| –ffile | get patterns from file instead of program | ||
| –Fc | separate fields with character c (default whitespace) | ||
| –v variable=value | assign value to variable (nawk only) | ||
| parameters | parameters have the format variable=expression
| files
| read standard input if files is – or no files are specified
| |
Program Format:
Patterns in program can be associated with a statement to perform if an input line matches the pattern. The format is:
{ statement }
A missing pattern always matches, and a missing statement prints the current input line.
Patterns:
| BEGIN | match before first input line |
| END | match after last input line |
| pattern1, pattern2, ..., patternn | match if pattern1, pattern2, or patternn match current input line |
| pattern1 && pattern2 | match if pattern1 and pattern2 match current input line |
| pattern1 || pattern2 | match if pattern1 or pattern2 match current input line |
| !pattern | match if pattern does not match current input line |
| /regular-expression/ | match if regular-expression matches current input line |
| relational-expression | match if relational-expression evaluates to true |
Flow Control Statements:
| break | exit from for or while loop |
| continue | execute next for or while loop |
| delete variable[expression] | delete element expression from array variable |
| do statement while (expression) | execute statement while expression is true |
| exit | skip remaining input |
| for (expression1; expression2; expression3) statement | execute statement while expression2 is true; loop is usually initialized with expression1 and incremented with expression3 |
| for (variable in array) statement | execute statement, setting variable to successive elements in array |
| if (expression) statement1 [ else statement2 ] | execute statement1 if expression is true, otherwise execute statement2 |
| next | skip rest of the input line |
| return[expression] | return value of expression |
| system(command) | execute command and return status |
| while (expression) statement | execute statement while expression is true |
Input/Output Statements:
| close(file) | close file |
| getline | set $0 to next input record (set NF, NR, FNR) |
| getline<file | set $0 to next input from file (set NF) |
| getline variable | set variable to next input record (set NR, FNR) |
| getline variable<file | set variable to next input record from file |
| command | getline | pipe output of command into getline |
| print current input record | |
| print expression | print expression; multiple expressions must be separated with a “,” |
| print expression>file | print expression to file; multiple expressions must be separated with a “,” |
| printf format expression | print expression according to C-like format. Multiple expressions must be separated with a “,”. Output can also be appended to file using >>, or piped to a command using |. |
| printf format expression>file | print expression to file according to C-like format. Multiple expressions must be separated with a “,”. Output can also be appended to file using >>, or piped to a command using |. |
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