Reading file in while loop bash scripting

问题

I've got this code which reads an example file of /etc/passwd:

#!/bin/bash

OLDIFS=$IFS
IFS=$'\n'

while read linea resto
do
        echo $linea
        echo $resto
        if [[ $(echo $linea | cut -d: -f6 | egrep -c 'al-03-04') == 1 ]]
        then
                finger $(cut -d: -f1) 2> fich
                if [[ $(egrep -c fich) == 1 ]]
                then
                        echo $(echo $linea | cut -d: -f1). Inactive user
                else
                        echo $(echo $linea | cut -d: -f1). Active user
                fi
        fi
done < <(cat fichpasswd)

IFS=$OLDIFS

and this is the example file of /etc/passwd:

jfer:x:5214:1007:Javier Lopez,,,:/home/al-03-04/jfer:/bin/bash
jperez:x:10912:1009:Juan Perez,,,:/home/al-03-04/jperez:/bin/bash
mfernan:x:10913:1009:Manuel Fernandez,,,:/home/al-02-03/mfernan:/bin/bash

The problem is that the while loop only reads the first line, ignoring the others. The script's output is:

jfer:x:5214:1007:Javier Lopez,,,:/home/al-03-04/jfer:/bin/bash

jfer. Active user

回答1:

You could try something like :

#!/bin/bash

FILE="test.txt"

while IFS=":" read -a data; do
  echo "${data[@]}"
  if [[ $(echo ${data[5]}|egrep -c 'al-03-04') -eq 1 ]]; then
    if [[ $(finger "${data[0]}" 2>&1) =~ "no such user" ]]; then
      echo "${data[0]}. Inactive user"
    else
      echo "${data[0]}. Active user"
    fi
  fi
done < "$FILE"

Here's the output :

ineumann ~ $ cat test.txt 
ineumann:x:5214:1007:Javier Lopez,,,:/home/al-03-04/jfer:/bin/bash
jperez:x:10912:1009:Juan Perez,,,:/home/al-03-04/jperez:/bin/bash
mfernan:x:10913:1009:Manuel Fernandez,,,:/home/al-02-03/mfernan:/bin/bash
ineumann ~ $ ./test.sh 
ineumann x 5214 1007 Javier Lopez,,, /home/al-03-04/jfer /bin/bash
ineumann. Active user
jperez x 10912 1009 Juan Perez,,, /home/al-03-04/jperez /bin/bash
jperez. Inactive user
mfernan x 10913 1009 Manuel Fernandez,,, /home/al-02-03/mfernan /bin/bash

A few comments on your script :

• No need to use cat to read your file in a loop.
• finger $(cut -d: -f1) 2> fich : cut need an input. And no need to use a temporary file to catch the output of finger (moreover this is not thread safe).
• No need to use cut in your script when you choose the right IFS to split a line in multiple parts. In your case, I think the smartest choice would be :.
• You can change the IFS only inside the loop with the syntax while IFS=':' read; do ...; done. No need to re-assign IFS with OLDIFS.
• You can also use the while IFS=':' read var1 var2 var3 trash; do ...; done syntax to avoid to use an array with read -a (but I'd prefer to use an array as I wrote in my version of your script).

来源：https://stackoverflow.com/questions/50886897/reading-file-in-while-loop-bash-scripting