Syntax in if-else block in bash shell script

Question

I'm pretty new to bash shell script, I have the following:

CMD_MYSQL="${MYSQL_DIR}mysql --user=${MYSQL_USER} --pass=${MYSQL_PASS} ..."

if [ ($CMD_MYSQL --execute="SELECT COUNT(*) FROM information_schema.tables WHERE \
  table_schema='$MYSQL_DB' and table_name='${tablename}_new';") -eq 1 ]; then
  ...
else
  echo "Table ${tablename}_new does not exist."
fi

You can safely ignore other variables.

I have syntax error near $CMD_MYSQL after if, I suppose because I try to call the variable $CMD_MYSQL. How should I fix this? Thanks.

try echo "$CMD_MYSQL --execute="RENAME TABLE $tablename to ${tablename}_old"; — Raghunandan Krishnamurthy
– Raghunandan Krishnamurthy, Commented Feb 5, 2014 at 7:42
@RaghunandanKrishnamurthy Sorry, not that $CMD_MYSQL. Please see edited. The syntax error is in the if condition. — Victor
– Victor, Commented Feb 5, 2014 at 7:44
do you want to use the return code of the output of mysql? in the former case you don't need square brackets and -eq in the latter - you are missing $ before (MYSQL — bobah
– bobah, Commented Feb 5, 2014 at 7:45

damienfrancois · Accepted Answer · 2014-02-05 07:50:54Z

1

I assume you want to test the output of the your command (and not its return code). Then the syntax should look like

CMD_MYSQL="${MYSQL_DIR}mysql --user=${MYSQL_USER} --pass=${MYSQL_PASS} ..."

if [ "$($CMD_MYSQL --execute="SELECT COUNT(*) FROM information_schema.tables WHERE \
  table_schema='$MYSQL_DB' and table_name='${tablename}_new';")" -eq 1 ]; then
  echo "Renaming ($MYSQL_DB.$tablename)..."
  $CMD_MYSQL --execute="RENAME TABLE $tablename to ${tablename}_old;"
else
  echo "Table ${tablename}_new does not exist."
fi

note the extra $ in front of the parentheses.

The parentheses, without $ in front, create a subshell. With the $, they substitute with the output of the command in the parentheses.

If your query does outputs a more complex result than just a number, you might need to search for the number inside the result with something like:

if [[ "$($CMD_MYSQL --execute="SELECT COUNT(*) FROM information_schema.tables WHERE \
  table_schema='$MYSQL_DB' and table_name='${tablename}_new';")" == *1* ]]; then
  echo "Renaming ($MYSQL_DB.$tablename)..."
  $CMD_MYSQL --execute="RENAME TABLE $tablename to ${tablename}_old;"
else
  echo "Table ${tablename}_new does not exist."
fi

edited Feb 5, 2014 at 7:50

answered Feb 5, 2014 at 7:44

damienfrancois

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2 Comments

damienfrancois Over a year ago

What does you query return exactly? If you get that error, it probably means your query returns several words, not a single number.

Victor Over a year ago

I guess I missed -N -s in my MySQL query. serverfault.com/a/334368/74192

Raghunandan Krishnamurthy · Accepted Answer · 2014-02-05 07:50:56Z

0

CMD_MYSQL="${MYSQL_DIR}mysql --user=${MYSQL_USER} --pass=${MYSQL_PASS} ..."

if [ "**$CMD_MYSQL --execute="SELECT COUNT(*) FROM information_schema.tables WHERE \
  table_schema='$MYSQL_DB' and table_name='${tablename}_new';**" -eq 1 ]; then
  echo "Table ${tablename}_new **does** exist."
else
  echo "Table ${tablename}_new does **not** exist."
fi

answered Feb 5, 2014 at 7:50

Raghunandan Krishnamurthy

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