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What are steps that a UNIX shell follows while processing a command?

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What are steps that a UNIX shell follows while processing a command?
posted Feb 27, 2016 by Mohammed Hussain

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1 Answer

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The sequence of executing commands by shell are as follows:

Parsing: The command is broke into words, by using the spaces as delimiters unless quoted. The tabs are replaced by a single space.

Evaluation of a variable: The words with $ as preceding character will be evaluted unless quoted.

Command Substitution: The commands surrounded by backquotes will be executed by the shell. Later these will be replaced into standard output of the command into command line.

Wild card interpretation: Finally, the shell identifies all the wild cards(?,*) in the command line and replaces the wild card with sorted list of file names which maches the pattern.

PATH evaluation: Ultimately shell looks for the PATH variable for the purpose of determining the sequence of directories to search for the files or commands.

answer Feb 27, 2016 by Shivaranjini
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+2 votes

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Can someone identify what's wrong in the regex, Please?

+1 vote

The command to convert from .xlsx to csv works in putty, but the same when given in informatica fails....I am getting exit error code 32512.

The workflowlog >>

Severity    Timestamp   Node    Thread  Message Code    Message
INFO    9/8/2016 5:28:20 PM Node_BIDEV  140284941813504 LM_36621    Command task instance [Convert_csv]: started command [convert], with pid [14121] on node [Node_BIDEV].
ERROR   9/8/2016 5:28:21 PM Node_BIDEV  140285390595840 LM_36623    Command task instance [Convert_csv]: execution of command [convert] did not complete successfully with exit code [32512]
WARNING 9/8/2016 5:28:21 PM Node_BIDEV  140285390595840 LM_36626    Command task instance [Convert_csv]: previous command [convert] failed and "run if previous command succeeded" option is set, the remaining commands will not be run.
ERROR   9/8/2016 5:28:21 PM Node_BIDEV  140285390595840 LM_36320    Command task instance [Convert_csv]: Execution failed.
WARNING 9/8/2016 5:28:21 PM Node_BIDEV  140285390595840 LM_36373    Workflow [wf_CUSTOMER_SURVEY_CORE_DailyFiles] is suspended.
INFO    9/8/2016 5:28:22 PM Node_BIDEV  140285390595840 LM_36375    Workflow [wf_CUSTOMER_SURVEY_CORE_DailyFiles]: Sent suspension email to email user 
WARNING 9/8/2016 5:28:27 PM Node_BIDEV  140284973283072 LM_36371    Workflow [wf_CUSTOMER_SURVEY_CORE_DailyFiles] is aborting.
WARNING 9/8/2016 5:28:27 PM Node_BIDEV  140284973283072 LM_36322    Workflow [wf_CUSTOMER_SURVEY_CORE_DailyFiles]: Execution aborted.

The command script I am using is

libreoffice --headless --convert-to csv:"Text - txt - csv (StarCalc)":"126,0,76,1,2" /var/opt/load/Sourcedata/CUSTOMER_SURVEY/2016Q2_ML_V1.xlsx

Please help me...

+1 vote

Is it possible to run a command and capture its output via an FD (like in proc_open()), but without using the shell? As far as I can see now there is no way to do it. I think that's a simple feature, maybe just add it to proc_open()? (for example run command directly using exec() if the first argument is an array?) it would be rational because there is already such option for Windows...

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