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Bash: How to read tab character when reading input

Hello,
i'm new to bash and searched the forum before asking this question. I'm reading input from a file line by line, however i need to check if the first string of a line is preceded by a tab. i'm using following code to read input line by line, but this ignores any whitespace/tab at the begining and end of the line. can anyone plz help me?

line=""

while read line
do parseLine $line;
done < <(cat $1)

"read" is already somewhat parsing the line in words. Tab being by default a separator is not making it to the line variable.

You can remove tab from the separators with using IFS=" ", or you can really read a better way the whole line with the "line" command:

while line=$(line)

You could use head to read a line.

Code:

line=$(head -n 1)

To verify that it includes tabs, you can pass it through od:

Code:

echo "$line" | od -tc

Which might output something like this:

Code:

0000000  h  e  l  l  o  \t  w  o  r  l  d  \n

0000014

thanks a lot for the replies. i'll try these out.

Quote:

Originally Posted by jlliagre

You can remove tab from the separators with using IFS=" ",

thanks a lot. this worked. sorry, but this will be my last question on this topic. now that i'm able to read characters how can can compare if the input read has tab?
i tried
if [ $1 = "\t" ]
it didn't work

A portable way would be:

Code:

if [ "$(expr $1 : '$.$'" = "<TAB>" ]

With bash, this should works too:

Code:

if [ "${1:0:1}" = "<TAB>" ]

Replace <TAB> with the tab character in the previous samples.

Hi.

Here is a script that illustrates the setting of TAB into a variable, the use of IFS to allow reading of TABS, and the test for a single TAB character ... cheers, makyo

Code:

#!/bin/sh



# @(#) s1      Demonstrate setting TAB into variable.



# Set tab character into variable, and verify it is there.

# Alternate method might be:

# mytab="      "

# where character between " " is typed (not copy/paste) as tab.

#

# Highlight characters by surrounding with innocuous ":".



mytab=`echo -e "\t"`

echo "The character :$mytab: is a tab." |

cat -tv



# Show how to use IFS for testing.  Loop forever until tab.

#

# Set Internal Field Separator to space only.



oldifs="$IFS"

IFS=" "



# Issue a prompt.



echo

echo " Enter data, only a single tab will cause end (or control-c)"



i=1

while :

do

        read line

        if [ "$line" = "$mytab" ]

        then

                echo " You entered a single TAB on iteration $i, done."

                exit 0

        else

                echo " Iteration $i, you entered :$line:, not a tab alone, continuing."

        fi

        i=`expr $i + 1`

done



IFS="$oldifs"



# Other work as necessary.



exit 0

thanks thanks thanks a lot to jlliagre and makyo. you guys really healped me. it worked!!! you guys are great. its tough being a newbie and help from ppl like you gets us going. thanks again.