Checking for certain characters - UNIX for Advanced & Expert Users

SAMZ · #1 07-17-2008

Could anyone help with the following enquiry.. i have a file in the following format:

ID .... VALUE
A001 .... 100
B002 .... 200
A004 .... 300
B006 .... 100
A997 .... 200
B776 .... 400

It is in a column format, but I want to check that the ID field always begins with with and A or B character this is my logic thus far:

If Character 1 DOES NOT equal A or B
then
display error message
else
carry on doing what you want
fi

not really sure how to chech that character 1 of each line does not equal A or B
habe tried following with no no joi

If [ ! grep '^A' $file || ! grep '^B' $file ] then
print "error"
else
print "it works"
fi

but the above does not work i believe it to logic as my unix understanding not great, please assist.

phemanth24 · #2 07-17-2008

Try this:

/(^A)|(^B)/ {num++}
END {if(num > 0);printf("%d instances of A,B exist\n", num);}

You can modify the output the way you want.

SAMZ · #3 07-17-2008

can't seem to get the above to work could you explain further please

phemanth24 · #4 07-17-2008

Hi Samz. I should have elaborated further.
I put my code into a script and ran it with awk.

Code:

awk -f <script name> <file>

Currently it prints the number of instances of A and B

phemanth24 · #5 07-17-2008

BTW, you could also bypass putting this into a script.

Code:

awk '/(^A)|(^B)/ {num++} END {if(num > 0);printf("%d instances of A,B exist\n", num);}' column

'column' is the file where I have the format you specified.

Diabolist · #6 07-17-2008

The input file:

Code:

$ cat ttt
ID .... VALUE
-------------
A001 .... 100
C003 .... 800
B002 .... 200
corrupt
data
A004 .... 300
C003 .... 800
foo .... bar

The script:

Code:

#!/bin/ksh

INPUT=ttt

{ while read LINE
do
  echo $LINE |egrep "^A|^B" > /dev/null 2>&1
  if [ $? -eq 0 ]
  then
    echo "Processing $LINE"
  else
    echo "Skipping $LINE"
  fi
done } < $INPUT

The output:

Code:

$ ./ttt.ksh
Skipping ID .... VALUE
Skipping -------------
Processing A001 .... 100
Skipping C003 .... 800
Processing B002 .... 200
Skipping corrupt
Skipping data
Processing A004 .... 300
Skipping C003 .... 800
Skipping foo .... bar

You could do a single string of commands using awk for the pattern matching, but I'm not sure how you want to process the line once you verify it's good... so this may offer the most flexibility.

Let us know if you need anything in the script explained.

SAMZ · #7 07-17-2008

Quote:

Originally Posted by phemanth24

BTW, you could also bypass putting this into a script.

Code:

awk '/(^A)|(^B)/ {num++} END {if(num > 0);printf("%d instances of A,B exist\n", num);}' column

'column' is the file where I have the format you specified.

Ok the above only tell me how many times A or B where in there. I require it to send an error message if a C exist or otherwise its fine to continue processing file.. hope that makes more sense

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