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I'm a beginner in bash scripting, and what I'm trying to is to build a script that is doing an API call to my enterprise system and returns the result to TXT file. In the end, I would like to read the output file that has been created by API. Unfortunately, it reads past file even if I'm removing it and I don't know why.

#!/bin/bash
#Clearing the history to check whether it helps or not
history -cw

#Defining variables
Scan_Output="Scan_output.txt"
Scan_Confirmation_Date=`awk 'NR==7' $Scan_Output` # reads line 7 from txt file
  
#Removing file if already exists
rm -f $Scan_Output

#API Request
curl "my piece of code" > $ScanOutput
sleep 5

echo $Scan_Confrimation_Date
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    You have a (probably) inconsequential typo between Scan_Confirmation_Date and Scan_Confrimation_Date. When you say your script "reads past the file", do you mean that you're getting something unexpected from the awk call to print line 7? Commented Aug 21, 2020 at 15:07
  • Hello Jeff - thank you for your answer. I would not say it's the typo. "Reads the past file" - I mean that the output was generated from a previous API call, let's say an hour ago but the new file contains current time but the awk reads the old time. When I will return to the bash console and exit VIM and perform the awk it will read the correct time from a file. Commented Aug 21, 2020 at 15:12
  • @Mateusz there is a typo in the Scan_Confrimation on the last line, and this is what JeffSchaller was pointing out Commented Aug 21, 2020 at 18:13

1 Answer 1

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Follow the order of operations in your code:

  1. Define an output file name

     Scan_Output="Scan_output.txt"

  2. Get the confirmation date from the file (this runs NOW)

     Scan_Confirmation_Date=`awk 'NR==7' $Scan_Output` # reads line 7 from txt file

  3. Remove the target file

     rm -f $Scan_Output

  4. Get some new data for the output file

     curl "my piece of code" > $ScanOutput

  5. Write the date we got back at the beginning of the script (and mind the spelling mistake in the variable name)

     echo $Scan_Confrimation_Date

I suspect you really meant to write this, but I'm not completely sure

#!/bin/bash
Scan_Output='Scan_output.txt'
curl "my piece of code" > "$ScanOutput"
Scan_Confirmation_Date=$(awk 'NR==7' "$Scan_Output")
printf "%s\n" "$Scan_Confirmation_Date"
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  • roaima - thank you! It is working well right now :) Would you please help me to understand why I cannot define Scan_Confirmation_Date variable before API request? Commented Aug 21, 2020 at 15:31
  • You defined it as the result of reading from the file you hadn't yet downloaded Commented Aug 21, 2020 at 15:52
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    @Mateusz The variable can be defined any time before use. But the command substitution (inside the backticks) is an initialiser which is run as soon as it is encountered. It does not define a command that will be invoked later, when the variable is referenced. Commented Aug 21, 2020 at 18:11

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