json1-4  Exercise 3: curl | jq, and Quoting in Three Shells
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Setup: srv.mjs (below) is a Node server on 127.0.0.1:8765. Run each part from its own shell (a PowerShell script started from Git Bash hung until its input was closed, and "cmd /c" from Git Bash started an interactive cmd).

--- srv.mjs ---
import http from 'node:http'; import fs from 'node:fs';
http.createServer((req, res) => {
  if (req.url === '/shop') { res.writeHead(200, { 'content-type': 'application/json' }); res.end(fs.readFileSync('shop.json')); }
  else if (req.url === '/missing') { res.writeHead(404, { 'content-type': 'application/json' }); res.end('{"error":"not found"}'); }
  else if (req.url === '/html') { res.writeHead(502, { 'content-type': 'text/html' }); res.end('<html>Bad Gateway</html>'); }
  else { res.writeHead(200); res.end('{"hello":"world"}'); }
}).listen(8765, '127.0.0.1');

--- ex3.sh (Git Bash) ---
# Exercise 3, part A (Git Bash): curl | jq against a local server, and what each failure looks like
export PATH="/c/lwdj/json/c4/bin:$PATH"
node srv.mjs & SP=$!; sleep 1
U=http://127.0.0.1:8765
echo '1. curl -s | jq'; curl -s $U/shop | jq -r '.products[].name' | tr '\n' ' '; echo
echo '2. curl WITHOUT -s, stderr merged into the pipe (2>&1)'; curl $U/hello 2>&1 | jq -c . 2>&1 | head -2
echo '3. 404 with a JSON error body, plain curl -s'; curl -s $U/missing | jq -c .; echo "   exits: curl ${PIPESTATUS[0]}, jq ${PIPESTATUS[1]}"
echo '4. same, curl -sf (fail on HTTP errors)'; curl -sf $U/missing | jq -c .; echo "   exits: curl ${PIPESTATUS[0]}, jq ${PIPESTATUS[1]}  (jq received nothing and printed nothing)"
echo '5. same, curl -s --fail-with-body'; curl -s --fail-with-body $U/missing | jq -c .; echo "   exits: curl ${PIPESTATUS[0]}, jq ${PIPESTATUS[1]}"
echo '6. 502 HTML page, curl -s'; curl -s $U/html | jq . 2>&1; echo "   exits: curl ${PIPESTATUS[0]}, jq ${PIPESTATUS[1]}"
echo '7. with pipefail, curl -sf'; ( set -o pipefail; curl -sf $U/missing | jq -c .; echo "   pipeline exit: $?" )
echo '8. keep the response, check the status, then parse'
code=$(curl -s -o body.tmp -w '%{http_code}' $U/missing); echo "   status $code"; [ "$code" = 200 ] && jq . body.tmp || { echo "   not 200, body was:"; cat body.tmp; echo; }
rm -f body.tmp
kill $SP 2>/dev/null; wait $SP 2>/dev/null

Output (part A):
1. curl -s | jq
Tea
 Coffee
 Biscuits
 Milk
 
2. curl WITHOUT -s, stderr merged into the pipe (2>&1)
jq: parse error: Invalid numeric literal at line 1, column 4
3. 404 with a JSON error body, plain curl -s
{"error":"not found"}
   exits: curl 0, jq 0
4. same, curl -sf (fail on HTTP errors)
   exits: curl 22, jq 0  (jq received nothing and printed nothing)
5. same, curl -s --fail-with-body
{"error":"not found"}
   exits: curl 22, jq 0
6. 502 HTML page, curl -s
jq: parse error: Invalid numeric literal at line 1, column 10
   exits: curl 0, jq 5
7. with pipefail, curl -sf
   pipeline exit: 22
8. keep the response, check the status, then parse
   status 404
   not 200, body was:
{"error":"not found"}

--- ex3.ps1 (Windows PowerShell 5.1) ---
# Exercise 3, part B (Windows PowerShell 5.1): the same filter, five ways to pass it
$env:Path = "C:\lwdj\json\c4\bin;" + $env:Path
Set-Location C:\lwdj\json\c4
"PowerShell " + $PSVersionTable.PSVersion
"1. single quotes, no inner quotes";            jq '.products[0].name' shop.json
"2. single quotes, inner double quotes";        jq '.products[] | select(.name == "Tea") | .sku' shop.json; "   exit " + $LASTEXITCODE
"3. inner quotes escaped with backslash";       jq '.products[] | select(.name == \"Tea\") | .sku' shop.json; "   exit " + $LASTEXITCODE
"4. --arg, no inner quotes at all";             jq --arg n Tea '.products[] | select(.name == $n) | .sku' shop.json; "   exit " + $LASTEXITCODE
"5. filter in a file with -f";                  Set-Content -Encoding ascii f.jq '.products[] | select(.name == "Tea") | .sku'; jq -f f.jq shop.json; "   exit " + $LASTEXITCODE
"6. pipe a PowerShell value in";                @{ a = 1; b = 'x' } | ConvertTo-Json -Compress | jq -c '.'

Output (part B):
PowerShell 5.1.26100.9549
1. single quotes, no inner quotes
"Tea"
2. single quotes, inner double quotes
jq: error: Tea/0 is not defined at <top-level>, line 1, column 31:
    .products[] | select(.name == Tea) | .sku
                                  ^^^
jq: 1 compile error
   exit 3
3. inner quotes escaped with backslash
"A1"
   exit 0
4. --arg, no inner quotes at all
"A1"
   exit 0
5. filter in a file with -f
"A1"
   exit 0
6. pipe a PowerShell value in
{"a":1,"b":"x"}

--- ex3.cmd (cmd.exe) ---
@echo off
rem Exercise 3, part C (cmd.exe)
set PATH=C:\lwdj\json\c4\bin;%PATH%
cd /d C:\lwdj\json\c4
echo 1. double quotes around the filter
jq ".shop" shop.json
echo 2. single quotes around the filter
jq '.shop' shop.json 2>&1 | findstr /n "error"
echo 3. inner quotes escaped with backslash
jq ".products[] | select(.name == \"Tea\") | .sku" shop.json
echo 4. --arg, no inner quotes at all
jq --arg n Tea ".products[] | select(.name == $n) | .sku" shop.json
echo 5. filter in a file with -f
jq -f f.jq shop.json

Output (part C):
1. double quotes around the filter
"Corner Shop"
2. single quotes around the filter
1:jq: error: syntax error, unexpected INVALID_CHARACTER, expecting end of file at <top-level>, line 1, column 1:
4:jq: 1 compile error
3. inner quotes escaped with backslash
"A1"
4. --arg, no inner quotes at all
"A1"
5. filter in a file with -f
"A1"

WHY THIS WORKS AS AN ANSWER
---------------------------
Part A shows that every curl|jq failure has a different signature. A 404 with a JSON body looks like success (both exit 0); curl -sf hides the body and exits 22 while jq, receiving nothing, still exits 0; --fail-with-body keeps the
body and exits 22; an HTML error page produces jq's "Invalid numeric literal" and exit 5; pipefail makes the pipeline report curl's 22; and the status-first form (-w '%{http_code}' into a variable) lets the script decide before parsing.
Case 2 shows why 2>&1 without -s is wrong: the progress meter text became part of jq's input. Parts B and C show quoting really differs: PowerShell 5.1 removes inner double quotes (the filter reached jq as ".name == Tea" and failed with
exit 3), cmd does not understand single quotes, and the two methods that work everywhere are --arg (no inner quotes needed) and -f (the shell never sees the filter). Windows PowerShell 5.1 only; PowerShell 7 was not tested.