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--- bash:parse_a_line_from_a_file [2019/12/07 01:42] – created peter
+++ bash:parse_a_line_from_a_file [2021/01/26 16:34] (current) – removed peter
@@ Line 1: / Line 1: @@
-====== BASH - Parse a line from a file ======
-There are many ways of doing this, depending on your needs.
-  * Simply print all lines containing the keyword test:
-    <code bash>grep test file.txt</code>
-  * The same but for many keywords.  Create a file that has all the keywords, one per line and run:
-    <code bash>grep -f keywords.txt file.txt</code>
-  * Process a file line by line, exit if the line is found:
-    <code bash>while read line; do echo $line | grep test && break; done < file.txt</code>
-  * Exit with status 1 if the line matches.  Unfortunately, if I remember correctly (not 100% sure), bash only allows you to set return values in functions.  So, to get an exit status you need to use something else.  Perl for example:
-    <code perl>perl -ne '/test/ && exit(1)' file.txt</code>
-  * Though you can't set an exit value, you can still do something similar with bash.  The exit value of the last command run is always saved as $? in bash, that means you can test the value of $? and act accordingly:
-<code bash>
-while read line; do let c++; echo $line | grep test >/dev/null;
-  if [[ $? == 0 ]] ; then echo Match for line $c : $line;
-  else echo No match for line $c; fi
-done < file.txt
-</code>
-===== Another approach to process a file line by line: =====
-<code bash>
-#!/bin/bash
-while IFS='' read -r line || [[ -n "$line" ]]; do
-    echo "Text read from file: $line"
-done < "$1"
-</code>
-===== Another Method =====
-Example file.
-<file>
-/17 21:04:01 sndc addr unit 1 : hu P1 (TempLinc)
-/17 21:04:02 sndc func StatusReq : hc P
-/17 21:04:04 rcvi addr unit 15 : hu P15 (TempAck_5)
-/17 21:04:04 rcvi func Preset : level 11
-/17 21:04:04 Temperature = 78 : hu P0 (office_temp)
-/17 21:19:01 sndc addr unit 1 : hu P1 (TempLinc)
-/17 21:19:02 sndc func StatusReq : hc P
-/17 21:19:05 rcvi addr unit 15 : hu P15 (TempAck_5)
-/17 21:19:05 rcvi func Preset : level 11
-/17 21:19:05 Temperature = 78 : hu P0 (office_temp)
-</file>
-<code>
-#!/bin/bash
-fil=/home/test.log
-# Test for existence of the test file
-if [ -f $fil ]
-then
-  # Read through the file looking for the word Temperature =
-  while read line
-  do
-    echo $line | grep -q Temperature
-    if [ $? == 0 ]; then
-    mytemp=`echo $line  | cut -d = -f2 | cut -d : -f1`
-    echo "Current temperature is: $mytemp"
-    fi
-  done < $fil
-fi
-</code>
-Returns:
-<code>
-Current temperature is:  78
-Current temperature is:  78
-</code>
-===== Only get last temperature record =====
-<code>
-#!/bin/bash
-fil=/home/heyu.log.ttyS0
-if [ -f $fil ]
-then
-mytemp=`grep Temperature $fil | tail -1 | cut -d = -f2 | cut -d : -f1`
-echo "Current temperature is: $mytemp"
-fi
-</code>