Command Reference Guide

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD

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

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ksh(1) ksh(1)

If a command which is a tracked alias is executed, and a command with the same name is installed in a

directory in the search path before the directory where the original command was found, the shell contin-

ues to load and execute the original command. Use the -t option of the alias command to correct this

situation.

If you move the current directory or one above it, pwd may not give the correct response. Use the cd

command with a full path name to correct this situation.

Some very old shell scripts contain a caret (ˆ) as a synonym for the pipe character (|). Note however,

ksh does not recognize the caret as a pipe character.

If a command is piped into a shell command, all variables set in the shell command are lost when the com-

mand completes.

Using the fc built-in command within a compound command causes the entire command to disappear

from the history ﬁle.

The built-in command . ﬁle reads the entire ﬁle before any commands are executed. Therefore, alias

and unalias commands in the ﬁle do not apply to any functions deﬁned in the ﬁle.

Traps are not processed while the shell is waiting for a foreground job. Thus, a trap on

CHLD is not exe-

cuted until the foreground job terminates.

The

export built-in command does not handle arrays properly. Only the ﬁrst element of an array is

exported to the environment.

Background processes started from a non-interactive shell cannot be accessed by using job control com-

mands.

In an international environment, character ordering is determined by the setting of

LC_COLLATE, rather

than by the binary ordering of character values in the machine collating sequence. This brings with it cer-

tain attendant dangers, particularly when using range expressions in ﬁle name generation patterns. For

example, the command,

rm [a-z]*

might be expected to match all ﬁle names beginning with a lowercase alphabetic character. However, if

dictionary ordering is speciﬁed by

LC_COLLATE,

it would also match ﬁle names beginning with an uppercase

character (as well as those beginning with accented letters). Conversely, it would fail to match letters col-

lated after

z in languages such as Danish or Norwegian.

The correct (and safe) way to match speciﬁc character classes in an international environment is to use a

pattern of the form:

rm [[:lower:]]*

This uses LC_CTYPE to determine character classes and works predictably for all supported languages and

codesets. For shell scripts produced on non-internationalized systems (or without consideration for the

above dangers), it is recommended that they be executed in a non-NLS environment. This requires that

LANG, LC_COLLATE, etc., be set to "C" or not set at all.

Be aware that the value of the IFS variable in the user’s environment affects the behavior of scripts.

ksh implements command substitution by creating a pipe between itself and the command. If the root ﬁle

system is full, the substituted command cannot write to the pipe. As a result, the shell receives no input

from the command, and the result of the substitution is null. In particular, using command substitution for

variable assignment under such circumstances results in the variable being silently assigned a

NULL value.

AUTHOR

ksh was developed by AT&T.

FILES

/etc/passwd to ﬁnd home directories

/etc/profile read to set up system environment

/etc/suid_profile security proﬁle

$HOME/.profile read to set up user’s custom environment

/tmp/sh ∗ for here-documents

HP-UX Release 11i: December 2000 − 22 − Section 1−−417

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