HP-UX Reference (11i v1 00/12) - 1 User Commands A-M (vol 1)

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD

/build/1111/BRICK/man1/!!!intro.1

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csh(1) csh(1)

ls -ld ˜paul

one could execute !{l}a to do

ls -ld ˜paula

while !la would look for a command starting with la.

Quoting with Single and Double Quotes

The quotation of strings by single quotes (’) and double quotes (" ) can be used to prevent all or some of the

remaining substitutions. Strings enclosed in single quotes are protected from any further interpretation.

Strings enclosed in double quotes are still variable- and command-expanded as described below.

In both cases the resulting text becomes (all or part of) a single word. Only in one special case (see Com-

mand Substitution below) does a double-quoted string yield parts of more than one word; single-quoted

strings never do.

Alias Substitution

csh maintains a list of aliases that can be established, displayed, and modiﬁed by the alias and

unalias commands. After a command line is scanned, it is parsed into distinct commands and the ﬁrst

word of each command, left-to-right, is checked to see if it has an alias. If it does, the text which is the

alias for that command is reread with the history mechanism available as if that command was the previ-

ous input line. The resulting words replace the command and argument list. If no reference is made to the

history list, the argument list is left unchanged.

Thus, if the alias for ls is ls -l, the command ls /usr maps to ls -l /usr

, leaving the argu-

ment list undisturbed. Similarly, if the alias for

lookup was grep !ˆ /etc/passwd , lookup

bill

maps to grep bill /etc/passwd .

If an alias is found, the word transformation of the input text is performed and the aliasing process begins

again on the re-formed input line. Looping is prevented if the ﬁrst word of the new text is the same as the

old by ﬂagging it to prevent further aliasing. Other loops are detected and cause an error.

Note that the mechanism allows aliasesto introduce parser metasyntax. Thus:

alias print ’pr \!* | lp’

makes a command that uses pr(1) to print its arguments on the line printer.

Expressions

Some of the built-in commands take expressions in which the operators are similar to those of C, with the

same precedence. These expressions appear in the @, exit, if, and while commands. The following

operators are available (shown in order of increasing precedence):

||&&|ˆ&==!==˜!˜<=>=<><<>>+-*/%!˜()

The following list shows the grouping of these operators. The precedence decreases from top to bottom in

the list:

*/%

<< >>

<= >= < >

== != =˜ !˜

The operators ==, !=, =˜, and !˜ compare their arguments as strings; all others operate on numbers.

The operators =˜ and !˜ are similar to != and ==, except that the right-hand side is a pattern (contain-

ing

*s, ?s, and instances of [...]) against which the left hand operand is matched. This reduces the need

for use of the switch statement in shell scripts when all that is really needed is pattern matching.

Strings beginning with 0 are considered octal numbers. Null or missing arguments are considered 0. The

result of all expressions are strings that represent decimal numbers. It is important to note that no two

components of an expression can appear in the same word. These components should be surrounded by

spaces except when adjacent to components of expressions that are syntactically signiﬁcant to the parser:

-, &, |, <, >, (, and ).

Also availablein expressions as primitive operands are command executions enclosed in curly braces ({})

and ﬁle enquiries of the form -l ﬁlename, where l is one of:

Section 1−−138 − 10 − HP-UX Release 11i: December 2000

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