02-02-2004
oreilly has a great book on regular expressions.
REGEX's are an essential to anyone scripting or programming.
as far as the pipe. just as was said in various other posts asking about the pipe. it takes the output from one command and feeds it into another command.
also if you are confused about what the line does the first place to start is by reading the man pages for each command used.
this should clear it up enuff so you can fill in the gaps and get a grasp on it.
Last edited by Optimus_P; 02-02-2004 at 10:45 AM..
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
OK, I am trying to become more familiar with grep and sed.
I have a file that is storing some records. I am allowing a user to
search for a keyword in the file with this:
grep -i "$keyword" testFile|sed -n -e 's/^/\
/' -e 's/:/\
/gp'
... (15 Replies)
Discussion started by: ericelysia
15 Replies
2. Shell Programming and Scripting
I have a file that contains many instances of double dollar signs. I want to use sed to get the first occurrence. for example, given the following data.
#Beginning of file
AB
34
$$
AB
$$
AB
98
$$
I only want to pull out:
AB
34
$$ (1 Reply)
Discussion started by: wxornot
1 Replies
3. UNIX for Dummies Questions & Answers
Hi All,
I have created a bourne script that basically wants to split a file up in to different parts. I have this working if the file has all the information on different lines but if it doesn't then it doesn't work.
i.e.
If this is the file
hello
12345
good bye
6789
I could grep all the... (5 Replies)
Discussion started by: jazz8146
5 Replies
4. UNIX for Dummies Questions & Answers
hello everybody!
I have a html file which is not properly formatted meaning that the whole content is in one line.
I want to to cut out certain parts of that file. Those parts are between ' #" ' and ' " ' and always start with ' sec_ ' and after the ' sec_ ' any number of characters and ' _... (2 Replies)
Discussion started by: MastaFue
2 Replies
5. Shell Programming and Scripting
HI all,
i have a line in a file it contains
Code:
one;two_1_10;two_2_10;two_3_10;three~
now i need to get the output as
Code:
one;two_1_abc_10;two_2_abc_10;two_3_abc_10;three~ ( 1 should be replaced with 1_abc for two__abc_10 , and one more thing the number of occurances of... (6 Replies)
Discussion started by: 2001.arun
6 Replies
6. Shell Programming and Scripting
So I have a html file with a bunch of words inside tags and I need to extract just the words, and I'm not sure exactly what the best way to do this is. The format is as follows:
<tr>
<td>word 1</td>
<td>word 2</td>
</tr>
And all I want to extract is the 'word 2'. First I tried... (3 Replies)
Discussion started by: flightskoo
3 Replies
7. Linux
I am stranded with a problem. Please solve.
How will you remove blank lines from a file using sed and grep? ( blank line contains nothing or only white spaces).
I run the below commands of sed and grep but grep isn't giving output as desired. Why?
sed '/^*$/d' blank
grep -v "^*$" blank... (3 Replies)
Discussion started by: ravisingh
3 Replies
8. Shell Programming and Scripting
Hi,
I have a file with reoccurring patterns and I want extract the 3rd line after the match, then delete another pattern from that third line.
For example the file is in the following format:
Hello
Name: Abc
Number: 123
Hello
Name: FQE
Number: 543
This occurs more than 100... (4 Replies)
Discussion started by: wsn
4 Replies
9. UNIX for Dummies Questions & Answers
Hello Everyone!
I'm kind of new to parsing and would like extract a partial part of my nmap scan output so I can convert it to csv/excel:
My current file has two types of lines like this:
Nmap scan report for dns1 (1.1.1.1)
Nmap scan report for dns2 (2.2.2.2)
Nmap scan report for 3.3.3.3
... (3 Replies)
Discussion started by: SarahS
3 Replies
10. Shell Programming and Scripting
Hi ,
I have a file where i have modifed certain things compared to original file . The difference of the original file and modified file is as follows.
# diff mir_lex.c.modified mir_lex.c.orig
3209c3209
< if(yy_current_buffer -> yy_is_our_buffer == 0) {
---
>... (5 Replies)
Discussion started by: breezevinay
5 Replies
POPEN(3) Linux Programmer's Manual POPEN(3)
NAME
popen, pclose - pipe stream to or from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(const char *command, const char *type);
int pclose(FILE *stream);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
popen(), pclose(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
The popen() function opens a process by creating a pipe, forking, and invoking the shell. Since a pipe is by definition unidirectional,
the type argument may specify only reading or writing, not both; the resulting stream is correspondingly read-only or write-only.
The command argument is a pointer to a null-terminated string containing a shell command line. This command is passed to /bin/sh using the
-c flag; interpretation, if any, is performed by the shell. The type argument is a pointer to a null-terminated string which must contain
either the letter 'r' for reading or the letter 'w' for writing. Since glibc 2.9, this argument can additionally include the letter 'e',
which causes the close-on-exec flag (FD_CLOEXEC) to be set on the underlying file descriptor; see the description of the O_CLOEXEC flag in
open(2) for reasons why this may be useful.
The return value from popen() is a normal standard I/O stream in all respects save that it must be closed with pclose() rather than
fclose(3). Writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the
process that called popen(), unless this is altered by the command itself. Conversely, reading from a "popened" stream reads the command's
standard output, and the command's standard input is the same as that of the process that called popen().
Note that output popen() streams are fully buffered by default.
The pclose() function waits for the associated process to terminate and returns the exit status of the command as returned by wait4(2).
RETURN VALUE
The popen() function returns NULL if the fork(2) or pipe(2) calls fail, or if it cannot allocate memory.
The pclose() function returns -1 if wait4(2) returns an error, or some other error is detected.
ERRORS
The popen() function does not set errno if memory allocation fails. If the underlying fork(2) or pipe(2) fails, errno is set appropri-
ately. If the type argument is invalid, and this condition is detected, errno is set to EINVAL.
If pclose() cannot obtain the child status, errno is set to ECHILD.
CONFORMING TO
POSIX.1-2001.
The 'e' value for type is a Linux extension.
BUGS
Since the standard input of a command opened for reading shares its seek offset with the process that called popen(), if the original
process has done a buffered read, the command's input position may not be as expected. Similarly, the output from a command opened for
writing may become intermingled with that of the original process. The latter can be avoided by calling fflush(3) before popen().
Failure to execute the shell is indistinguishable from the shell's failure to execute command, or an immediate exit of the command. The
only hint is an exit status of 127.
SEE ALSO
sh(1), fork(2), pipe(2), wait4(2), fclose(3), fflush(3), fopen(3), stdio(3), system(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/.
GNU
2010-02-03 POPEN(3)