UNIX for Dummies Questions & Answers

1) The square brackets ensure * is a literal not a wild card metacharacter.

2) Using boolean as procedural control of flow amuses some, but I like to use procedural language for control of flow, for maintainability. Isn't the new version max plus 1?

3) ${0##*/} says take $0, pound really hard on the nose until it is removed down to the last slash, or in other words, basename, entry name of $0. One # means pound soft, stop at first / or whatever follows. The alternative operator is %, as in you get your percent in the end, so it beats on the end not not nose. The directory containing $0 would be ${0%/*}, take off the end to the first /. Of course, if $0 has no /, that malfunctions.

4) Not standard output >&1 or nothing, but standard error >&2 Printf takes first a template (usage) with meta-strings in it that say where to insert the additional parameters. Printf "A%sC", "B" prints ABC.

I'm not sure if this comment was directed at my suggestion to eliminate the ls|head pipeline. For the record, I am not on a mission to get rid of pipelines. And, when speed isn't a critical issue in a shell script, I sometimes use a pipeline (even when avoiding it could produce faster code) if the pipeline is "easier to read and understand."

But, when globbing could yield a fork error due to ARG_MAX limits, and an ls -t | head -1 pipeline would sometimes yield the wrong file and result in the destruction of data, I much prefer a different solution that avoids both issues.

Note also that the basename and dirname utilities aren't quite as easy to replace as you're suggesting. The commands:

Code:

ddir=$(dirname "$1")
sdir=${1%/*}
bbase=$(basename "$1")
sbase=${1##*/}
printf "directory containing \"%s\" is \"%s\" or \"%s\"\n" "$1" "$ddir" "$sdir"
printf "last component of \"%s\" is \"%s\" or \"%s\"\n" "$1" "$bbase" "$sbase"

show that they produce identical results when this script is invoked with the name of my home directory:

Code:

directory containing "/Users/dwc" is "/Users" or "/Users"
last component of "/Users/dwc" is "dwc" or "dwc"

but, very different results if I invoke the same script with / as an operand:

Code:

directory containing "/" is "/" or ""
last component of "/" is "/" or ""

I can certainly modify the script above to check for the special case when the operand is root; but I will frequently use basename and dirname because I don't have to think about the special case (even though a fork and exec is involved). And, what is going on will be more obvious to naive readers of my code. If this is done once during the initialization of a long running script, I might not care about the small additional start up costs. However, if this were to be done every time in a tight loop processing thousands of files that might include "/", it would be a different issue.

Yes, '/' is often a painful exception in many algorithms! People who enter directories with a trailing '/' can also mess you up. For instance, on some systems "find /tmp/" produces paths like "/tmp//xxx". Of course, you can clean then with ${xxx%/} if they are not '/' (root).

I put the code you provided in version.sh and calling that script from another script "callversion.sh"

callversion.sh

Code:

#!/bin/bash
. /home/infrmtca/bin/dwh_Loadfuncs.sh
. /home/infrmtca/bin/version.sh 30
echo $NEW_FILE_NAME

And when i run the script "callversion.sh" it is giving me the following output, How can i make it print "version.sh" instead of "callversion.sh". I guess i don't have any other simple option other than replacing the {0##*/} with actual script name. please let me know if this is possible any other means. Thank you.

Code:

Usage: callversion.sh Provider_Code
        Provider_Code "30" unknown
Valid Provider_Code values are:
Provider_Code   Provider
=============   ============
         1      AAC
         4      AGFIRST
         5      AGRIBANK
         6      COBANK
         7      COLUSA-GLENN
         8      FCSA
        11      HAWAII
        12      IDAHO
        16      FCBTEXAS
        17      WAC
        18      AGVANTIS
        20      YOSEMITE
        21      FPI

move the file to that name.

callversion.sh is invoking the version.sh, those are 2 different scripts i want the script to print it as version.sh instead of callversion.sh, if i move it i will replace one with another.

if version calls callversion, you could source it instead (. filename), and then $0 would be version. Better is to make the callversion bits functions inside version, either explicitly or by sourcing the callversion file that is rewritten to be all functions.