The IFS variable is used in as the input field separator. If you set IFS to | (i.e. IFS=| ), | will be treated as delimiters between words/fields when splitting a line of input. [donotprint]
| Tutorial details | |
|---|---|
| Difficulty | Easy (rss) |
| Root privileges | No |
| Requirements | None |
| Time | 2m |
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cat -etv <<<"$IFS"
Sample outputs:
^I$ $
In this example, read first and last name using read command and set IFS to a white space:
IFS=' ' read -p 'Enter your first and last name : ' first last echo "Hello, $first $last" |
Sample outputs:
Enter your first and last name : Vivek Gite Hello, Vivek Gite
In this example set IFS to | and read data:
IFS='|' read domain ip4 ip6 <<< 'google.com|74.125.236.65|2404:6800:4007:801::1008' echo "$domain has $ip4 IPv4 and $ipv6 IPv6 address." |
Sample outputs:
google.com has 74.125.236.65 IPv4 and IPv6 address.
while loop example with IFS and read command
Create a text file (named foo.txt) as follows:
$ cat foo.txt
Sample outputs:
google.com|74.125.236.65|2404:6800:4007:801::1008 i.theos.in|58.27.86.81|2600:807:320:305::3f6e:f648 cyberciti.biz|75.126.153.206|2600:807:320:305::3f6e:f649
Create a bash shell script as follows:
#!/bin/bash _input="foo.txt" # set IFS (internal field separator) to | # read file using while loop while IFS='|' read -r domain ip4 ip6 do echo "$domain has $ip4 IPv4 and $ip6 IPv6 address." done < "$_input" |
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Thx Vivek, i use custom IFS sometimes when i do bash scripts, but i’ve never had the idea to include it directly inside the while loop !
That easy, quick, efficient and class, just what i like.
Thx for the tips.
Pierre B.
Hi Vivek,
I did try to apply this trick to one of my script, but it seems that specifying the IFS this way broke something, when i put it back as it was before : it works again.
Here is the function where i do use the custom IFS :
Log_Chk() { # Usage: $0 called with the "log name" as $@ (as a list) #+ Note :only the "esmlog" is checked by this function, as it the only relevant log for hardware components status DOMAIN="ESMLOG" PrintDomainStart ${DOMAIN} OLD_IFS=$IFS # backup the default IFS while read line ; do # Set IFS to its new value, defined by the "cdv" value IFS=";" omconfig preferences cdvformat delimiter=semicolon &>/dev/null # Set the "semicolon" as the "cdv" read Status Data_or_Date Description <</dev/null elif [[ "${Status}" = 'Non-Critical' ]] ; then PrintWarning "${Description:0:22}... @ ${Data_or_Date#[[:upper:]][[:alpha:]][[:alpha:]][[:space:]]}" "${Status}" "1" && RETCODE="${NonCritical}" 2>/dev/null elif [[ "${Status}" = 'Ok' ]] ; then PrintOk "${Description:0:22}... @ ${Data_or_Date#[[:upper:]][[:alpha:]][[:alpha:]][[:space:]]}" "${Status}" "1" # Do nothing ! fi done << EOF $(omreport system esmlog -fmt cdv |tail -10 |grep -E "^(Ok|Non-Critical|Critical)") EOF IFS=$OLD_IFS # Back to default IFS PrintDomainEnd return $RETCODE }Ok, i finally change that piece of *** i posted for something cleaner, and then it works.
Just in case i post it there :
Log_Chk() { # Usage: $0 called with the "log name" as $@ (as a list) #+ Note :only the "esmlog" is checked by this function, as it the only relevant log for hardware components status if [[ "${ChassisModel}" =~ 'R710' ]] ; then DOMAIN="ESMLOG" log="esmlog" else DOMAIN="ALERTLOG" log="alertlog" fi PrintDomainStart ${DOMAIN} while IFS=";" read Status Data_or_Date Description ; do omconfig preferences cdvformat delimiter=semicolon &>/dev/null # Set the "semicolon" as the "cdv" if [[ "${Status}" = 'Critical' ]] ; then PrintFailure "${Description:0:24}... @ ${Data_or_Date#[[:upper:]][[:alpha:]][[:alpha:]][[:space:]]}" "${Status}" "1" && declare -r RETCODE="${Critical}" 2>/dev/null elif [[ "${Status}" = 'Non-Critical' ]] ; then PrintWarning "${Description:0:24}... @ ${Data_or_Date#[[:upper:]][[:alpha:]][[:alpha:]][[:space:]]}" "${Status}" "1" && RETCODE="${NonCritical}" 2>/dev/null elif [[ "${Status}" = 'Ok' ]] ; then PrintOk "${Description:0:24}... @ ${Data_or_Date#[[:upper:]][[:alpha:]][[:alpha:]][[:space:]]}" "${Status}" "1" fi done <<<"$(omreport system "${log}" -fmt cdv |tail -10 |grep -E "^(Ok|Non-Critical|Critical)" |tac)" PrintDomainEnd return $RETCODE }Just a side note:
with cat, both -e and -t specifies -v implicitly.
So you’re actually specifying -v three times.
cat -etv = cat -et
There is a typo in this example, ip6 will not give an output since you define $ipv6
Thanks for the heads up!
Dear ViVek,
Thank you ! \o/