Bash 脚本 - 检查文件是否包含特定行

Question

I need to check if a file contains a specific line. This file is written continuously by someone, so I put the check inside a while loop.

FILE="/Users/test/my.out"
STRING="MYNAME"
EXIT=1
while [ $EXIT -ne 0 ]; do 
    if [ -f $FILE ] ; then CHECK IF THE "STRING" IS IN THE FILE - IF YES echo "FOUND"; EXIT=0; fi
done

The file contains text and multiple lines.

Answer 1

如果$FILE包含文件名并且$STRING包含要搜索的字符串，那么您可以使用以下命令显示文件是否匹配：

if [ ! -z $(grep "$STRING" "$FILE") ]; then echo "FOUND"; fi

Answer 2

Poll the file's modification time and grep for the string when it changes:

while :; do
    a=$(stat -c%Y "$FILE") # GNU stat
    [ "$b" != "$a" ] && b="$a" && \
        grep -q "$STRING" "$FILE" && echo FOUND
    sleep 1
done

Note: BSD users should use stat -f%m

Answer 3

Try:

while : ;do
    [[ -f "$FILE" ]] && grep -q "$STRING" "$FILE" && echo "FOUND" && break
done

This will loop continuously without waiting, you may want to add a waiting period (eg 5 seconds in this example):

while : ;do
    [[ -f "$FILE" ]] && grep -q "$STRING" "$FILE" && echo "FOUND" && break
    sleep 5
done

Answer 4

A more rigorous check to test if a given line $STRING is contained in a file FILE would be

awk '$0 == "'${STRING}'"' $FILE

This in particular addresses my concerns with @fstab's answer (which also applies to all other previous answers): It checks the complete line and not just for substring presence within a line (as done with the grep solutions from above).

The loop could be done as shown in the other answers.

Answer 5

I had to add ssh keys to the authorized_keys file from a script. I've found two options (the bad and the ugly :)):

for f in "$tmp/keys/"*; do
    line=`cat "$f"`
    dst_line=`fgrep "$line" "$home/.ssh/authorized_keys" || true`
    if [ "$line" != "$dst_line" ]; then
        echo "$line" >> "$home/.ssh/authorized_keys"
    fi
done

for f in "$tmp/keys/"*; do
    cat "$f" >> "$home/.ssh/authorized_keys"
done
cat "$home/.ssh/authorized_keys" | sort | uniq > "$home/.ssh/authorized_keys.new"
chmod 0600 "$home/.ssh/authorized_keys.new"
chown "$user:" "$home/.ssh/authorized_keys.new"
mv "$home"/.ssh/authorized_keys.new \
    "$home"/.ssh/authorized_keys

I thought with uniq it would be more concise, but it turned out that it's not. And the need to adjust the permissions... And the order of the lines changes... Doesn't look good.

Answer 6

Turning this comment into an answer since it seems to do what I expect (from what I understand of the original question):

cat <<EOF | grep -Fx "${search_term}"
hello
world
EOF

• Searching for hello or world succeeds
• Searching for ello or worl fails

Answer 7

From the grep's man:

-q, --quiet, --silent
    Quiet; do not write anything to standard output.  Exit immediately with zero status if any match is found, even if an error was detected.  Also see the -s or --no-messages option.
-F, --fixed-strings
    Interpret PATTERNS as fixed strings, not regular expressions.
-x, --line-regexp
    Select only those matches that exactly match the whole line.  For a regular expression pattern, this is like parenthesizing the pattern and then surrounding it with ^ and $.

# Inline
grep -q -F "$STRING" "$FILE" && echo 'Found' || echo 'Not Found'
grep -q -F "$STRING" "$FILE" || echo 'Not Found'

# Multiline
if grep -q -F "$STRING" "$FILE"; then
  echo 'Found'
else
  echo 'Not Found'
fi

if ! grep -q -F "$STRING" "$FILE"; then
  echo 'Not Found'
fi

If you need to check the whole line use -x flag:

grep -q -x -F "$STRING" "$FILE" && echo 'Found' || echo 'Not Found'