A little help please Post: 302145626

Sponsored Content

Top Forums Shell Programming and Scripting A little help please Post 302145626 by porter on Wednesday 14th of November 2007 09:36:26 PM

11-14-2007

Registered User

Quote:

Originally Posted by immyakram

I believe this can done by using the echo function by getting the line from $1 and then inserting it into $2 bu cant quite put my finger on it.

That is the essential nub of the problem. For instance, lastline would be a piece of cake

Code:

#!/bin/sh
echo "$1" >>"$2"

because the >> operator appends the data. But this problem says we have to put the data as a new first line.

So my solution says, okay I know what the contents of the new file should look like

Code:

echo "$1" | cat - "$2"

but that output just dissappears, so we need to put it somewhere, like a temporary file, here $$ will be used as a temporary file as it's a unique number, ie the pid of the shell.

Code:

echo "$1" | cat - "$2" >$$

but the problem says that this new output should be in the original file, so what we do is rename this temporary file to the original file name, which as a byproduct is (a) atomic (b) unlinks the original file

Code:

mv $$ $2

Does that help?

Now tell me any down sides of my solution... Smilie

porter

View Public Profile for porter

Find all posts by porter

LEARN ABOUT FREEBSD

atf-sh

ATF-SH(1)						    BSD General Commands Manual 						 ATF-SH(1)

NAME

     atf-sh [-s shell] -- interpreter for shell-based test programs

SYNOPSIS

     atf-sh script

DESCRIPTION

     atf-sh is an interpreter that runs the test program given in script after loading the atf-sh(3) library.

     atf-sh is not a real interpreter though: it is just a wrapper around the system-wide shell defined by ATF_SHELL.  atf-sh executes the inter-
     preter, loads the atf-sh(3) library and then runs the script.  You must consider atf-sh to be a POSIX shell by default and thus should not
     use any non-standard extensions.

     The following options are available:

     -s shell	  Specifies the shell to use instead of the value provided by ATF_SHELL.

ENVIRONMENT

     ATF_LIBEXECDIR    Overrides the builtin directory where atf-sh is located.  Should not be overridden other than for testing purposes.
     ATF_PKGDATADIR    Overrides the builtin directory where libatf-sh.subr is located.  Should not be overridden other than for testing purposes.
     ATF_SHELL	       Path to the system shell to be used in the generated scripts.  Scripts must not rely on this variable being set to select a
		       specific interpreter.

EXAMPLES

     Scripts using atf-sh(3) should start with:

	   #! /usr/bin/env atf-sh

     Alternatively, if you want to explicitly choose a shell interpreter, you cannot rely on env(1) to find atf-sh.  Instead, you have to hardcode
     the path to atf-sh in the script and then use the -s option afterwards as a single parameter:

	   #! /path/to/bin/atf-sh -s/bin/bash

ENVIRONMENT

     ATF_SHELL	  Path to the system shell to be used in the generated scripts.

SEE ALSO

     atf-sh(3)

BSD
								September 27, 2014							       BSD