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Top Forums UNIX for Dummies Questions & Answers [Solved] Problem bash if file exists then < do...> else <do...> Post 302813321 by Don Cragun on Monday 27th of May 2013 05:07:09 AM
Old 05-27-2013
Quote:
Originally Posted by beca123456
Hi !

I have a problem with an if/else statement in bash.
I want to check if the file exists before running a task (for example here, counting lines), and if not I need to create an empty output file
Code:
if [ -f /input.tab ]
then
wc -l input.tab > output.temp
else
>output.temp
fi

The problem is even if the condition is true (the file actually exists) it goes directly to the else part and create an empty file in any case.

Could someone explain me what is wrong with my syntax... Smilie!!!
Does the file input.tab really exist in the root directory (/input.tab), or is it in the current directory (input.tab)? It would seem that you should use the same pathname in both the test and the wc commands.
This User Gave Thanks to Don Cragun For This Post:
 

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newform(1)						      General Commands Manual							newform(1)

NAME
newform - change or reformat a text file SYNOPSIS
[file]... DESCRIPTION
reads lines from the named files, or standard input if no input file is named, and reproduces the lines on standard output. Lines are reformatted in accordance with command line options in effect. Command line options can appear in any order, can be repeated, and can be intermingled with the optional files. Command line options are processed in the order specified. This means that option sequences such as yield results different from Options are applied to all files on the command line. Options recognizes the following options: Same as except characters are appended to the end of a line. Truncate n characters from the beginning of the line when the line length is greater than the effective line length (see The default is to truncate the number of characters necessary to obtain the effective line length. The default value is used when with no n is used. This option can be used to delete the sequence numbers from a COBOL program as follows: The must be used to set the effective line length shorter than any existing line in the file so that the option is activated. Change the prefix/append character to k. The default character for k is a space. Same as except that characters are truncated from the end of the line. Write the tab specification format line on the standard output before any other lines are output. The tab specification format line which is printed will correspond to the format specified in the option. If no option is specified, the line which is printed contains the default specification of Input tab specification: expands tabs to spaces, according to the tab specifications given. The tabspec recognizes all tab specification forms described in tabs(1). In addition, tabspec can be in which assumes that the tab specification is to be found in the first line read from the standard input (see fspec(4)). If no tabspec is given, tabspec defaults to A tabspec of expects no tabs; if any are found, they are treated as Set the effective line length to n characters. If n is not entered, defaults to 72. The default line length without the option is 80 characters. Note that tabs and backspaces are treated as single characters (use to expand tabs to spaces). Output tab specification: replaces spaces with tabs, according to the tab specifications given. The tab specifications are the same as for If no tabspec is given, tabspec defaults to A tabspec of means that no spaces will be converted to tabs on output. Prefix n characters (see to the beginning of a line when the line length is less than the effective line length. The default is to prefix the number of characters necessary to obtain the effective line length. Shear off leading characters on each line up to the first tab and place up to 8 of the sheared characters at the end of the line. If more than 8 characters (not counting the first tab) are sheared, the eighth character is replaced by a and any characters to the right of it are discarded. The first tab is always discarded. An error message and program exit occur if this option is used on a file without a tab on each line. The characters sheared off are saved internally until all other options specified are applied to that line. The characters are then added at the end of the processed line. For example, to convert a file with leading digits, one or more tabs, and text on each line, to a file beginning with the text, all tabs after the first expanded to spaces, padded with spaces out to column 72 (or truncated to column 72), and the leading digits placed starting at column 73, the command would be: RETURN VALUE
returns one of the following values: No errors encountered. An error occurred. DIAGNOSTICS
All diagnostics are fatal. was called with a bad option. There was no tab on one line. Self-explanatory. A line exceeds 512 characters after being expanded in the internal work buffer. A tab specification is incorrectly formatted, or specified tab stops are not ascending. A tabspec read from a file (or standard input) must not contain a tabspec referencing another file (or standard input). WARNINGS
normally only keeps track of physical characters; however, for the and options, keeps track of backspaces in order to line up tabs in the appropriate logical columns. does not prompt the user if a tabspec is to be read from the standard input (by use of or If the option is used, and the last option specified was and was preceded by either a or a the tab specification format line will be incor- rect. SEE ALSO
csplit(1), tabs(1), fspec(4). newform(1)
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