How to Tail -F the Latest Log File with a Given Pattern

How to tail -f the latest log file with a given pattern

[Edit: after a quick googling for a tool]

You might want to try out multitail - http://www.vanheusden.com/multitail/

If you want to stick with Dennis Williamson's answer (and I've +1'ed him accordingly) here are the blanks filled in for you.

In your shell, run the following script (or it's zsh equivalent, I whipped this up in bash before I saw the zsh tag):

#!/bin/bash

TARGET_DIR="some/logfiles/"
SYMLINK_FILE="SoftwareLog.latest"
SYMLINK_PATH="$TARGET_DIR/$SYMLINK_FILE"

function getLastModifiedFile {
    echo $(ls -t "$TARGET_DIR" | grep -v "$SYMLINK_FILE" | head -1)
}

function getCurrentlySymlinkedFile {
    if [[ -h $SYMLINK_PATH ]]
    then
        echo $(ls -l $SYMLINK_PATH | awk '{print $NF}')
    else
        echo ""
    fi
}

symlinkedFile=$(getCurrentlySymlinkedFile)
while true
do
    sleep 10
    lastModified=$(getLastModifiedFile)
    if [[ $symlinkedFile != $lastModified ]]
    then
        ln -nsf $lastModified $SYMLINK_PATH
        symlinkedFile=$lastModified
    fi
done

Background that process using the normal method (again, I don't know zsh, so it might be different)...

./updateSymlink.sh 2>&1 > /dev/null

Then tail -F $SYMLINK_PATH so that the tail hands the changing of the symbolic link or a rotation of the file.

This is slightly convoluted, but I don't know of another way to do this with tail. If anyone else knows of a utility that handles this, then let them step forward because I'd love to see it myself too - applications like Jetty by default do logs this way and I always script up a symlinking script run on a cron to compensate for it.

[Edit: Removed an erroneous 'j' from the end of one of the lines. You also had a bad variable name "lastModifiedFile" didn't exist, the proper name that you set is "lastModified"]

How to follow (tail -f) the latest file (matching a pattern) in a directory and call as alias with parameter

tail -f "$(find . -maxdepth 1 -name "logfile*" -printf "%Ts/%f\n" | sort -n | tail -1 | cut -d/ -f2)"

Tail the result of the find command. Search for files prefixed with logfile in the current directory and print the epoch time of creation as well as the file path and name, separated by a forward slash Pipe this through to sort and then print the latest entry with tail -1 before stripping out to to leave only the file path with cut.

Do a tail -F until matching a pattern

Try this:

sh -c 'tail -n +0 -f /tmp/foo | { sed "/EOF/ q" && kill $$ ;}'

The whole command-line will exit as soon as the "EOF" string is seen in /tmp/foo.

There is one side-effect: the tail process will be left running (in the background) until anything is written to /tmp/foo.

Tail -f - Show last X lines that match a pattern

grep PATTERN FILE | tail -n10; tail -f -n0 FILE | grep PATTERN;

Tail -f search file with * match and latest date time

Use

tail -f $(ls -t /var/log/impala/impalad.demo.local.impala.log.INFO.* | head -1)

instead. tail expects a file to read from, which you obtain with ls -t /var/log/impala/impalad.demo.local.impala.log.INFO.* | head -1. Piping follows an input | output pattern, though, so your current scheme won't get you far. Piping the filename into tail won't work either because tail doesn't expect filenames from standard input. To pass a filename to tail you must pass it as an argument.

How to tail all the log files inside a folder and subfolders?

To log all the files inside a folder, you can go to the folder and write

tail -f *.log

To add the subfolders to the tailf command, use

tail -f **/*.log

Of course, the regular expression can be improved to match only specific file names.

Bash : How to tail latest file in continuous loop

#!/bin/bash
#      ^^^^ -- **NOT** /bin/sh

substring=";A database exception has occurred: FATAL DBERR:  SQL_ERROR: ORA-00001: unique constraint (IX_TEST1) violated"
newest=
timeout=10  # number of seconds of no input after which to look for a newer file

# sets a global shell variable called "newest" when run
# to keep overhead down, this avoids invoking any external commands
find_newest() {
  set -- "${DIR?The variable DIR is required}"/env/log/LOG*
  [[ -e $1 || -L $1 ]] || return 1
  newest=$1; shift
  while (( $# )); do
    [[ $1 -nt $newest ]] && newest=$1
    shift
  done
}

while :; do
  find_newest  # check for newer files
  # if the newest file isn't the one we're already following...
  if [[ $tailing_from_file != "$newest" ]]; then
    exec < <(tail -f -- "$newest")  # start a new copy of tail following the newer one
    tailing_from_file=$newest       # and record that file's name
  fi
  if read -t "$timeout" -r line && [[ $line = *"$substring"* ]]; then
    echo "Do something here"
  fi
done

Shell function to tail a log file for a specific string for a specific time

#!/bin/bash
tail -f logfile | grep 'certain_word' | read -t 1200 dummy_var
[ $? -eq 0 ]  && echo 'ok'  || echo 'server not up'

This reads anything written to logfile, searches for certain_word, echos ok if all is good, otherwise after waiting 1200 seconds (20 minutes) it complains.

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