an "and" operator for "if" statement
I'm trying to create a simple bash script to check if the website is down and for some reason the "and" operator doesn't work:
#!/usr/bin/env bash
WEBSITE=domain.com
SUBJECT="$WEBSITE DOWN!"
EMAILID="an@email.com"
STATUS=$(curl -sI $WEBSITE | awk '/HTTP/1.1/ { print $2 }')
STRING=$(curl -s $WEBSITE | grep -o "string_to_search")
VALUE="string_to_search"
if [ $STATUS -ne 200 ] && [[ "$STRING" != "$VALUE" ]]; then
echo "Website: $WEBSITE is down, status code: '$STATUS' - $(date)" | mail -s "$SUBJECT" $EMAILID
fi
The "-a" operator also doesn't work:
if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]]
Could you also please advise when to use:
What you have should work, unless $STATUS is empty. It would probably be better to do:
if ! [ "$STATUS" -eq 200 ] 2> /dev/null && [ "$STRING" != "$VALUE" ]; then
or
if [ "$STATUS" != 200 ] && [ "$STRING" != "$VALUE" ]; then
It's hard to say, since you haven't shown us exactly what is going wrong with your script.
Personal opinion: never use [[ . It is not portable to different shells.
尝试这个：
if [ $STATUS -ne 200 -a "$STRING" != "$VALUE" ]; then
Quote:
The "-a" operator also doesn't work:
if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]]
For a more elaborate explanation: [ and ] are no bash reserved words. The if keyword introduces a conditional to be evaluated by a job (the conditional is true if the job's return value is 0 or false otherwise).
For trivial tests, there is the test program ( man test ).
As some find lines like if test -f filename; then foo bar; fi if test -f filename; then foo bar; fi if test -f filename; then foo bar; fi etc. annoying, on most systems you find a program called [ which is in fact only a symlink to the test program. When test is called as [ , you have to add ] as the last positional argument.
So if test -f filename is basically the same (in terms of processes spawned) as if [ -f filename ] . In both cases the test program will be started, and both processes should behave identically.
Here's your mistake: if [ $STATUS -ne 200 ] -a [[ "$STRING" != "$VALUE" ]] will parse to if + some job, the job being everything except the if itself. The job is only a simple command (bash speak for something which results in a single process), which means the first word ( [ ) is the command and the rest its positional arguments. There are remaining arguments after the first ] .
Also not, [[ is indeed a bash keyword but in this case it's only parsed as a normal command argument because it's not at the front of the command.
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