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* psql: print values and return the COUNT(*) value to bash?
@ 2025-12-29 07:21 Ron Johnson <[email protected]>
2025-12-29 08:12 ` Re: psql: print values and return the COUNT(*) value to bash? Jehan-Guillaume de Rorthais <[email protected]>
2025-12-29 10:11 ` Re: psql: print values and return the COUNT(*) value to bash? hubert depesz lubaczewski <[email protected]>
0 siblings, 2 replies; 3+ messages in thread
From: Ron Johnson @ 2025-12-29 07:21 UTC (permalink / raw)
To: pgsql-general
Currently I do this in a bash script:
Tbl=table_1
Fld=field_1
Sql="SELECT CURRENT_TIMESTAMP - MIN($Fld) AS days_ago
, MIN($Fld) as oldest_date
, COUNT(*) AS cnt
FROM $Tbl;"
psql -h <host> <db> -Xc "${Sql}"
days_ago | oldest_date | cnt
----------+-------------+-----
| | 0
(1 row)
More stuff happens after this. I want to print out these four lines, but
also test the COUNT(*) value and bypass other bash commands if the count ==
0.
Is there any relatively simple way to do this (psql print and return
count(*))?
--
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: psql: print values and return the COUNT(*) value to bash?
2025-12-29 07:21 psql: print values and return the COUNT(*) value to bash? Ron Johnson <[email protected]>
@ 2025-12-29 08:12 ` Jehan-Guillaume de Rorthais <[email protected]>
1 sibling, 0 replies; 3+ messages in thread
From: Jehan-Guillaume de Rorthais @ 2025-12-29 08:12 UTC (permalink / raw)
To: Ron Johnson <[email protected]>; +Cc: pgsql-general
On Mon, 29 Dec 2025 02:21:41 -0500
Ron Johnson <[email protected]> wrote:
…
> More stuff happens after this. I want to print out these four lines, but
> also test the COUNT(*) value and bypass other bash commands if the count ==
> 0.
You should probably output your result from psql in a parsable way (CSV ? TSV ?
custom ?) for your bash script, then print values from bash. The commands
"column" or "printf" could help you format a pretty table if really needed.
> Is there any relatively simple way to do this (psql print and return
> count(*))?
Not in a clean way. To make psql return something else than 0, you need to
trigger an error with a failing query to make it return 3 when ON_ERROR_STOP is
enabled.
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: psql: print values and return the COUNT(*) value to bash?
2025-12-29 07:21 psql: print values and return the COUNT(*) value to bash? Ron Johnson <[email protected]>
@ 2025-12-29 10:11 ` hubert depesz lubaczewski <[email protected]>
1 sibling, 0 replies; 3+ messages in thread
From: hubert depesz lubaczewski @ 2025-12-29 10:11 UTC (permalink / raw)
To: Ron Johnson <[email protected]>; +Cc: pgsql-general
On Mon, Dec 29, 2025 at 02:21:41AM -0500, Ron Johnson wrote:
> Currently I do this in a bash script:
> Tbl=table_1
> Fld=field_1
> Sql="SELECT CURRENT_TIMESTAMP - MIN($Fld) AS days_ago
> , MIN($Fld) as oldest_date
> , COUNT(*) AS cnt
> FROM $Tbl;"
> psql -h <host> <db> -Xc "${Sql}"
> days_ago | oldest_date | cnt
> ----------+-------------+-----
> | | 0
> (1 row)
>
> More stuff happens after this. I want to print out these four lines, but
> also test the COUNT(*) value and bypass other bash commands if the count ==
> 0.
>
> Is there any relatively simple way to do this (psql print and return
> count(*))?
1. Don't interpolate $variables to your sql. Instead use -v "t=$Tbl" -v
"f=$Fld" options to psql, and then make your query use :"t" and :"f"
- it's safer.
2. Catch output of the psql to variable, and check last line, there is
rowcount there.
Example:
=$ cat z.sh
#!/usr/bin/env bash
table=pg_stat_all_tables
field=last_autovacuum
returned="$( psql -d depesz_explain -v "t=$table" -v "f=$field" -X << _SQL_
select current_timestamp - min(:"f") as days_ago
, min(:"f") as oldest_date
, count(*) as cnt
from :"t"
_SQL_
)"
row_count="$( tail -n1 <<< "${returned}" | tr -cd 0-9 )"
echo "Rowcount = $row_count"
echo "Full output:"
echo "${returned}"
# vim: set filetype=bash shiftwidth=4 expandtab smarttab softtabstop=4 tabstop=4 textwidth=132 :
=$ bash z.sh
Rowcount = 1
Full output:
days_ago | oldest_date | cnt
------------------------+-------------------------------+-----
7 days 03:48:07.348247 | 2025-12-22 07:22:32.593814+01 | 212
(1 row)
Best regards,
depesz
^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2025-12-29 10:11 UTC | newest]
Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed)
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2025-12-29 07:21 psql: print values and return the COUNT(*) value to bash? Ron Johnson <[email protected]>
2025-12-29 08:12 ` Jehan-Guillaume de Rorthais <[email protected]>
2025-12-29 10:11 ` hubert depesz lubaczewski <[email protected]>
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