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Test Your Knowledge in Computers #914
Difficulty: Medium
In bash, grep -v -e '^[[:space:]]*$' file.txt will filter all the blank lines from file.txt and save the results in a file called file.txt.
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mktemp(3) [v7 man page]

MKTEMP(3)						     Library Functions Manual							 MKTEMP(3)

NAME
mktemp - make a unique file name SYNOPSIS
char *mktemp(template) char *template; DESCRIPTION
Mktemp replaces template by a unique file name, and returns the address of the template. The template should look like a file name with six trailing X's, which will be replaced with the current process id and a unique letter. SEE ALSO
getpid(2) MKTEMP(3)

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MKTEMP(3)						     Linux Programmer's Manual							 MKTEMP(3)

NAME
mktemp - make a unique temporary file name SYNOPSIS
#include <stdlib.h> char *mktemp(char *template); DESCRIPTION
The mktemp() function generates a unique temporary file name from template. The last six characters of template must be XXXXXX and these are replaced with a string that makes the filename unique. Since it will be modified, template must not be a string constant, but should be declared as a character array. RETURN VALUE
The mktemp() function returns NULL on error (template did not end in XXXXXX) and template otherwise. If the call was successful, the last six bytes of template will have been modified in such a way that the resulting name is unique (does not exist already). If the call was unsuccessful, template is made an empty string. ERRORS
EINVAL The last six characters of template were not XXXXXX. CONFORMING TO
BSD 4.3. POSIX dictates tmpnam(3). NOTE
The prototype is in <unistd.h> for libc4, libc5, glibc1; glibc2 follows the Single Unix Specification and has the prototype in <stdlib.h>. BUGS
Never use mktemp(). Some implementations follow BSD 4.3 and replace XXXXXX by the current process id and a single letter, so that at most 26 different names can be returned. Since on the one hand the names are easy to guess, and on the other hand there is a race between test- ing whether the name exists and opening the file, every use of mktemp() is a security risk. The race is avoided by mkstemp(3). SEE ALSO
mkstemp(3), tempnam(3), tmpfile(3), tmpnam(3) GNU
1993-04-03 MKTEMP(3)

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