Script parameters in Bash

Question

I m trying to make a shell script which should be used like this   ocrscript sh -from  home kristoffer test png -to  home kristoffer test txt   The script will then ocr convert the image file to a text file  Here is what I have come up with so far      bin bash export HOME  home kristoffer  usr local bin abbyyocr9 -rl Swedish -if    fromvalue    -of    tovalue    2 gt  amp 1   But I don t know how to get the -from and -to values  Any ideas on how to do it

User · Answer

In bash  1 is the first argument passed to the script   2 second and so on   usr local bin abbyyocr9 -rl Swedish -if   1  -of   2  2 gt  amp 1   So you can use     your script sh some source file png destination file txt   Explanation on double quotes   consider three scripts     foo sh bash bar sh  1    cat foo2 sh bash bar sh   1     bar sh echo  1- 1   2- 2    Now invoke     bash foo sh  a b  1-a 2-b    bash foo2 sh  a b  1-a b 2-   When you invoke foo sh  a b  then it invokes bar sh a b  two arguments   and with foo2 sh  a b  it invokes bar sh  a b   1 argument   Always have in mind how parameters are passed and expaned in bash  it will save you a lot of headache

User · Answer

Use the variables   1     2     3  and so on to access arguments  To access all of them you can use       or to get the count of arguments     might be useful to check for too few or too many arguments

User · Answer

I needed to make sure that my scripts are entirely portable between various machines  shells and even cygwin versions  Further  my colleagues who were the ones I had to write the scripts for  are programmers  so I ended up using this   for   i 1 i lt     i       do      if      i     -s         then   i              var1    i        elif      i     -log         then   i              logFile    i          elif      i     -x         then   i              var2    i            elif      i     -p          then   i              var3    i        elif      i     -b         then   i              var4    i        elif      i     -l         then   i              var5    i         elif      i     -a         then   i              var6    i       fi  done    Rationale  I included a launcher sh script as well  since the whole operation had several steps which were quasi independent on each other  I m saying  quasi   because even though each script could be run on its own  they were usually all run together   and in two days I found out  that about half of my colleagues  being programmers and all  were too good to be using the launcher file  follow the  usage   or read the HELP which was displayed every time they did something wrong and they were making a mess of the whole thing  running scripts with arguments in the wrong order and complaining that the scripts didn t work properly  Being the choleric I am I decided to overhaul all my scripts to make sure that they are colleague-proof  The code segment above was the first thing

User · Answer

If you re not completely attached to using  from  and  to  as your option names  it s fairly easy to implement this using getopts   while getopts f t  opts  do    case   opts  in       f  FROM VAL   OPTARG           t  TO VAL   OPTARG        esac done   getopts is a program that processes command line arguments and conveniently parses them for you    f t  specifies that you re expecting 2 parameters that contain values  indicated by the colon   Something like f t v says that -v will only be interpreted as a flag   opts is where the current parameter is stored  The case statement is where you will process this     OPTARG  contains the value following the parameter    FROM VAL  for example will get the value  home kristoffer test png if you ran your script like   ocrscript sh -f  home kristoffer test png -t  home kristoffer test txt  As the others are suggesting  if this is your first time writing bash scripts you should really read up on some basics  This was just a quick tutorial on how getopts works

User · Answer

The arguments that you provide to a bashscript will appear in the variables  1 and  2 and  3 where the number refers to the argument   0 is the command itself   The arguments are seperated by spaces  so if you would provide the -from and -to in the command  they will end up in these variables too  so for this     ocrscript sh -from  home kristoffer test png -to  home kristoffer test txt   You ll get    0      ocrscript sh  1      -from  2       home kristoffer test png  3      -to  4       home kristoffer test txt   It might be easier to omit the -from and the -to  like   ocrscript sh  home kristoffer test png  home kristoffer test txt   Then you ll have    1       home kristoffer test png  2       home kristoffer test txt   The downside is that you ll have to supply it in the right order  There are libraries that can make it easier to parse named arguments on the command line  but usually for simple shell scripts you should just use the easy way  if it s no problem   Then you can do    usr local bin abbyyocr9 -rl Swedish -if   1  -of   2  2 gt  amp 1   The double quotes around the  1 and the  2 are not always necessary but are adviced  because some strings won t work if you don t put them between double quotes

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