[[ ]] and [ ] work similar, but the implementation is different.
The [ is a builtin command. In fact it is an alias of the test command. (When run as [ the last argument must be ]. Command arguments may be redirected with < and >, and that is what caused your problem. The redirection can be prevented by quoting "<"">" or \<\>, but the standard operators are -lt and -gt. As with all command arguments, you should use "quotes" to prevent word splitting and globbing.
The [[ ]] is a compound, built into the shell interpreter. Because it is not a command, its content can be freely designed, and in fact a < and > are valid integer comparators. And the values are not subject to globbing, and word splitting happens before variable substitution (i.e. you need to quote "two words" to be seen as one value but not $word even if it's value is "two words").
These 2 Users Gave Thanks to MadeInGermany For This Post:
Hi,
I'm trying to use sed within a shell script (bash, running ubuntu). The command works fine from the command line, but when I use it within the script, rather than creating a file with the name I've specified, it creates one that ends with a question mark '?' when you use ls, e.g.... (3 Replies)
I have a script that runs ditto for me, and occasionally (if I exit the script while ditto is running in the background) it will leave an empty file named 0 in the script's directory. The next time I run the script, it generates incorrect data because of this file. I know I can easily insert a... (1 Reply)
I have a script that runs ditto for me, and occasionally (if I exit the script while ditto is running in the background) it will leave an empty file named 0 in the script's directory. The next time I run the script, it generates incorrect data because of this file. I know I can easily insert a... (1 Reply)
Hi All,
I have a script that does daily checks on my storage environment and is run from an AIX host.
The script currently works great but I have been changing and updating bits of it to make it easier for my lesser colleagues to understand :p
However now with the updates I have made I... (1 Reply)
I'm working on a project that requires me to compress then relocate directories to a different location based on their last date of modification. After running the script I check to see if it worked, and upon unzipping the tar.gz using I created everything that should be there is. I then performed... (4 Replies)
Hi,
I am trying to create a lock file with the following code but for some reason after file is created it has
wrong name "PASP?.lock??"
Please let us know how to get rid of these '??' from file name and from where they are coming?
#!/bin/ksh... (6 Replies)
I am new to Linux. Using latest version of Ubuntu.
I want to make a script that creates a 1GB file filled with zeros using dd and then formats the file as vfat with a label of "MYFILE".
If anyone can help me it would be appreciated. (9 Replies)
I have the following script
#!/bin/sh
Usage () {
echo "Usage: $0 <config_file>"
echo "Example: ./sftp_ondemand_daily.sh /export/data/mbsesb/config/ond
emand.cfg /export/data/mbsesb/config/filename.lst"
exit 1
}
if
then
Usage
fi
... (6 Replies)
I am new to Linux. Using latest version of Ubuntu.
I want to make a script that creates a 1GB file filled with zeros using dd and then formats the file as vfat with a label of "MYFILE".
If anyone can help me it would be appreciated. (1 Reply)
Discussion started by: amandasaza08
1 Replies
LEARN ABOUT SUSE
wordfree
WORDEXP(3) Linux Programmer's Manual WORDEXP(3)NAME
wordexp, wordfree - perform word expansion like a posix-shell
SYNOPSIS
#include <wordexp.h>
int wordexp(const char *s, wordexp_t *p, int flags);
void wordfree(wordexp_t *p);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
wordexp(), wordfree(): _XOPEN_SOURCE
DESCRIPTION
The function wordexp() performs a shell-like expansion of the string s and returns the result in the structure pointed to by p. The data
type wordexp_t is a structure that at least has the fields we_wordc, we_wordv, and we_offs. The field we_wordc is a size_t that gives the
number of words in the expansion of s. The field we_wordv is a char ** that points to the array of words found. The field we_offs of type
size_t is sometimes (depending on flags, see below) used to indicate the number of initial elements in the we_wordv array that should be
filled with NULLs.
The function wordfree() frees the allocated memory again. More precisely, it does not free its argument, but it frees the array we_wordv
and the strings that points to.
The string argument
Since the expansion is the same as the expansion by the shell (see sh(1)) of the parameters to a command, the string s must not contain
characters that would be illegal in shell command parameters. In particular, there must not be any unescaped newline or |, &, ;, <, >, (,
), {, } characters outside a command substitution or parameter substitution context.
If the argument s contains a word that starts with an unquoted comment character #, then it is unspecified whether that word and all fol-
lowing words are ignored, or the # is treated as a non-comment character.
The expansion
The expansion done consists of the following stages: tilde expansion (replacing ~user by user's home directory), variable substitution
(replacing $FOO by the value of the environment variable FOO), command substitution (replacing $(command) or `command` by the output of
command), arithmetic expansion, field splitting, wildcard expansion, quote removal.
The result of expansion of special parameters ($@, $*, $#, $?, $-, $$, $!, $0) is unspecified.
Field splitting is done using the environment variable $IFS. If it is not set, the field separators are space, tab and newline.
The output array
The array we_wordv contains the words found, followed by a NULL.
The flags argument
The flag argument is a bitwise inclusive OR of the following values:
WRDE_APPEND
Append the words found to the array resulting from a previous call.
WRDE_DOOFFS
Insert we_offs initial NULLs in the array we_wordv. (These are not counted in the returned we_wordc.)
WRDE_NOCMD
Don't do command substitution.
WRDE_REUSE
The argument p resulted from a previous call to wordexp(), and wordfree() was not called. Reuse the allocated storage.
WRDE_SHOWERR
Normally during command substitution stderr is redirected to /dev/null. This flag specifies that stderr is not to be redirected.
WRDE_UNDEF
Consider it an error if an undefined shell variable is expanded.
RETURN VALUE
In case of success 0 is returned. In case of error one of the following five values is returned.
WRDE_BADCHAR
Illegal occurrence of newline or one of |, &, ;, <, >, (, ), {, }.
WRDE_BADVAL
An undefined shell variable was referenced, and the WRDE_UNDEF flag told us to consider this an error.
WRDE_CMDSUB
Command substitution occurred, and the WRDE_NOCMD flag told us to consider this an error.
WRDE_NOSPACE
Out of memory.
WRDE_SYNTAX
Shell syntax error, such as unbalanced parentheses or unmatched quotes.
VERSIONS
wordexp() and wordfree() are provided in glibc since version 2.1.
CONFORMING TO
POSIX.1-2001.
EXAMPLE
The output of the following example program is approximately that of "ls [a-c]*.c".
#include <stdio.h>
#include <stdlib.h>
#include <wordexp.h>
int
main(int argc, char **argv)
{
wordexp_t p;
char **w;
int i;
wordexp("[a-c]*.c", &p, 0);
w = p.we_wordv;
for (i = 0; i < p.we_wordc; i++)
printf("%s
", w[i]);
wordfree(&p);
exit(EXIT_SUCCESS);
}
SEE ALSO fnmatch(3), glob(3)COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2008-07-14 WORDEXP(3)